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Digitized by the Internet Archive 
in 2011 with funding from 
The Library of Congress 



http://www.archive.org/details/hydrologyfundameOOmead 




High Falls on the Peshtigo River, Wisconsin, before Development. 
( E. C. Wild. ) 




The Hydro-Electric Development at High Falls. Building Located at Foot of 
I- ormer Fall. Power Transmitted to Green Bay, Wisconsin, a Distance of 
about Sixty-two Miles. 



HYDROLOGY 



THE FUNDAMENTAL BASIS OF HYDRAULIC 

ENGINEERING 



BY 

DANIEL W. MEAD 

Member American Society of Civil Engineers 

Consulting Engineer 

Professor Hydraulic and Sanitary Engineering 

University of Wisconsin 



McGRAW-HILL BOOK COMPANY, Inc. 
239 West 39TH Street. New York 



LONDON: HILL PUBLISHING CO., Ltd. 

6 & 8 BOUYERIE ST., E. C. 

1919 












Copyrighted 1917-1919 

BY 

DANIEL W. MEAD 



OCi 2u 1919 



Blied Printing company. Madison. 



A535 308 



PREFACE 

In the following" pages the author has discussed some of the most 
important facts and principles of hydrology. The author believes, 
from his observations during more than 35 years of professional prac- 
tice, that more failures have resulted in various hydraulic engineering 
projects from lack of adequate conceptions, on the part of the design- 
ing engineers, of the fundamental principles of hydrology and of the 
importance of hydrological factors than from defects in structural 
design. In many cases the engineer has based his work on unwarranted 
assumptions and has not possessed sufficient knowledge even to ap- 
preciate the necessity of hydrological investigations. 

As a result of the lack of appreciation of the importance of the 
fundamental basis on which every sound hydraulic project must rest, 
numerous irrigation projects, water power plants and public water 
works have proved partial or complete failures for lack of adequate 
water supplies, life and property have been destroyed by failures of 
dams, inadequate reservoir spillways and protecting works, and drain- 
age and flood protection enterprises have been undertaken with no 
adequate knowledge of necessary flood capacities. In many ways un- 
necessary losses are frequently entailed which have been largely due 
to the fact that the importance of hydrological information has not 
been sufficiently impressed upon the minds of hydraulic engineers. 

The author has made no attempt in the following pages to furnish 
categorical answers to complex hydrological questions but has en- 
deavored to show that the answers to the same questions may be and 
sometimes are reversed under different local conditions, and are always 
greatly modified thereby. He has found it necessary in almost every 
chapter to warn the engineer against attempts to solve hydrological 
problems by formulas or rules of thumb of restricted application and 
to insist in every case upon the necessity of conclusions based upon 
the detailed consideration of all the local factors in each problem. 

While the author has emphasized the impossibility of a high degree 
of accuracy in the solution of most hydrological problems, he has also 
attempted to show that such problems are susceptible of a solution 
fully as accurate as in the case of most other engineering problems. 

While hydrology is by no means a new subject it has received far 
less study and attention than its importance warrants. Some of the 
phenomena have been discussed in treatises on water supply and 
sewerage, but the subject has been introduced as a separate technical 
study in engineering schools only within the last fifteen vears. 



vi Preface. 

In 1904 the author issued his "Notes on Hydrology" as a basis for 
a course of study at the University of Wisconsin but it was found to 
be not wholly satisfactory and has long since been out of print. The 
present work is the result of notes derived from both investigation and 
practice and has been prepared primarily for the author's classes in 
the University of Wisconsin. Nothing is introduced which the author 
has not found to be of practical importance in his own professional 
work, and much has been omitted on account of the necessary limita- 
tions of this volume. The literature on the subject is very extensive, 
and a carefully selected list of the most important sources of informa- 
tion has been added to each chapter. 

It is perhaps needless to call attention to the necessity of much 
further investigation and study in order to correlate correctly many 
of the intricate factors of hyclrological problems and to make their 
true relations manifest. On the subject of stream flow, one of the 
most intricate of these problems, the various methods of correlation 
which have been suggested by various hydrologists are shown in order 
to explain both their strength and weakness, and in order to indicate 
the desirable direction of further investigations. The methods used 
and suggested by the author for the solution of stream flow problems 
are not offered as final methods but simply as the best practical methods 
which in his judgment have been devised up to the present time. 

The author has endeavored to give credit to the source of all illus- 
trations and methods in connection with their presentation. He ac- 
knowledges his indebtedness to the technical press and to various reports, 
technical works and society proceedings to which reference has been 
made. His acknowledgments are especially due to Mr. L. R. Balch 
for material assistance in the preparation of this volume, particularly 
in connection with the editorial work. Acknowledgments for valuable 
suggestions are also due to the author's associates, Messrs. C. V. 
Seastone and F. W. Scheidenhelm. 

DANIEL W. MEAD 
Madison, Wisconsin, September, 1919. 



CONTENTS 

CHAPTER I 

Introduction 

Hydrology — Prevalence of Law in all Natural Phenomena — Hydrological 
Influence on Early Settlement — Effect of Development on Imporatnce 
of the Subject — Basis of Present Engineering Practice — Extent of 
Knowlelge necessary for Successful Engineering Work — Casualties 
Due to Lack of Hydrological Knowledge — Variations in Hydrological 
Phenoment — Factors of Safety in Engineering Work — Fundamental 
Laws — Complexity of Influences — Sources and Limitations of Hy- 
drological Knowledge — Determination of Hydrological Relations — 
Danger of General Conclusions — Purpose of the Study of Hydrology — 
Study of Hydrological Literature — References to Failures in Hy- 
draulic Engineering Works — Literature 1 

CHAPTER II 

Water — Its Occurrence, Utilization axd Control 

Importance of Hydrological Conditions — The Occurrence of Water — Cir- 
culation — The Cleansing and Transporting Work of Water — Precipi- 
tation — Surface Waters — Ground Waters — Water Supplies — Control 
of Water — Necessity for the Study of Hydrology — Literature 23 

CHAPTER III 

Some Fundamental Theories 

Growth and Development — Past Conditions and Their Evolution — Funda- 
mental Considerations — The Atmosphere — Atmospheric Tempera- 
tures — .Atmospheric Pressures — The Planetary Circulation — Litera- 
ture 43 

CHAPTER IV 

Winds and Storms 

Permanent Winds — Peoriodic Winds — Non-Periodic or Irregular Winds — 
Cyclones and Anticyclones — The Translation of Storm Centers — 
Storm Movements — Local Wind Movements — Tornadoes — Hurricanes 
and Typhoons — Hurricane Movements — Cold Waves — Hot Waves — 
Hydrological Effects of the Winds — Weather Forecasting — Literature 59 

CHAPTER V 

Hydrography 

Ocean Currents — Lake Currents — Vertical Lake Currents — Tides — Wind 
Tides — Seiches — Waves — Wave Motion — Height of Oscillating Waves 
— Length and Velocity of Oscillating Waves — Energy and Pressure of 
Waves — Effects of Waves — Literature 89 



viii Contents. 

CHAPTER VI 

Atmospheric Moisture and Evaporation 

Atmospheric Moisture — Tension and Weight — Atmospheric Temperatures 
and Moisture at High Altitudes — Geographical Distribution of Nor- 
mal Atmospheric Moisture — Variation in Absolute and Relative 
Humidity — Interchange of Moisture Between Air and Land or Water 
Surface — Heat Changes Involved in Evaporation and Condensation — 
Evaporation — Factors of Evaporation — Vapor Tension — Tempera- 
tures — Wind Movements — Effect of Altitude on Factors of Evapora- 
tion — Evaporation of Snow and Ice — Evaporation from Land — Effects 
of Vegetation — General Principles — Measurements of Atmospheric 
Moisture and Evaporation — Importance of a Knowledge of Evapora- 
tion and Atmospheric Moisture in Engineering Studies — General 
Conclusions — Literature 112 

CHAPTER VII 

Precipitation 

Precipitation — The Ultimate Source of- all. Water Supplies — The Practical 
Consideration of Rainfall — Causes which Produce or Influence Pre- 
cipitation — Sources of Atmospheric Moisture — Geographical and To- 
pographical Conditions Affecting Precipitation — Precipitation in Re- 
lation to Location near Bodies of Water and Tracks of Cyclonic 
Storms — Occurrence and Distribution of Rain Storms — Effects of Al- 
titude on Precipitation — Minor Influences — Rainfall Maps — Occur- 
rence of Precipitation — Rainfall Accompanying West Indian Hurri- 
cane — Rainfall Accompanying General Cyclonic Storms — Thunder 
Storms — Annual Expectancy of Storms — Artificial -Production of 
Rain — Literature 15G 

CHAPTER VIII 

Rainfall Measurements and records 

The Measurement of Precipitation, instruments Used — Exposure of Rain 
Gages — Location of Rain Gages of the United States Weather Bureau 
—The Effect of Wind— Records of Rainfall of the United States- 
Dependability of Precipitation Records — Estimating Rainfall on any 
Area — Literature 187 

CHAPTER IX 

Annual Rainfall in the United States and its Variation 

Quantity and Distribution of Average Annual Rainfall — Variation in 
Annual Precipitation — Variation in Annual Rainfall in Limited 
Areas — Variation in Local Annual Rainfall — Detail Study of Local 
Variation in Annual Precipitation — Cycles in Rainfall — Extreme 
Variations in Local Annual Rainfall — Expectancy of Future Rain- 
fall Occurrences — Rainfall Data and the Law of Probabilities — Ap- 
plication of Probability Calculations — Literature 200 



Contents. 1X 

CHAPTER X 

Seasonal Rainfall in the United States and its Variation 

Seasonal Variation in Rainfall-Local Variations in Seasonal Distribu 
tion of Rainfall— Mass Diagram of Rainfall— Seasonal Divisions of 
the Year for Agricultural .Purposes— Further Analysis of Rainfall for 
Utilitarian Purposes-Seasonal Rainfall as Affecting Stream Flow 220 

CHAPTER XI 

Great Rainfalls 

Importance of the Study of Great Rainfalls-Great Rainfalls-Limita- 
tions of Information-Sources of Information-Frequency of Intense 
Rainfalls— Local Intensities of Short Duration— Frequency of In- 
tense Storms of Short Duration— Approximate Maximum Intensities 
of Short Storms-Studies of Local Intensity— Rainfall for Longer 
Periods— Intensity over Large Areas— Excessive Rainfall of the East- 
ern United States— The Application of Data— Frequency of Storms 
of Various Magnitudes— Time— Area— Depth Curves for Major 
Storms— The Study of Extreme Conditions of Rainfall— General 

Conclusions — Literature 

CHAPTER XII 
Rainfall and Altitude 

Importance of Subject-General Considerations— Factors Affecting 
Amount of Precipitation— Southern California— Southern Arizona- 
North Eastern Utah— The Relations of Altitude and Rainfall During 
Single Storms— Rules for Estimating Relations of Altitude to Rain- 
fall — General Conclusions— Literature 2S " 

CHAPTER XIII 

Geological Agencies and Their Work 

Hvdrological Influence of Topography and Geology— Outline of Causes 
Productive of Topographical and Geological Changes— Rock Structure 
and Texture— Erosion— Weathering— Corrasion— Erosion by Wave 
Action— Glacial Erosion— Movements of the Earth's Crust— Results 
of Erosion— Origin and Development of Drainage Valleys— Origin 
of Falls and Rapids— The Origin of Lakes— Permanency of Lakes- 
Changes in the Extent of Lands— Literature 309 

CHAPTER XIV 
Geology 
Object of the Study of Geology— Rock Masses and Their General Classifi- 
cation—Historical Geology— Chronological Order of Geological 
Time— Division of Strata— The Precambrian Rocks— The Upper 
Mississippi Valley— The Cambrian Period— The Ordovician Period— 
The Silurian Period— The Devonian period— Carboniferous Period- 
Sedimentary Deposits of Later Periods— General Characteristics of 



x Contents. 

the Strata — Modifications of the Strata— iPre-Glacial Drainage — 
The Glacial Period — Work of Glaciers — Glacial Recession— Glacial 
Drainage — Post — Glacial Drainage — Hydrological Conditions — Gen- 
eral Geology and Physiography — Investigation of Geological. Con- 
ditions — Literature 352 

CHAPTER XV 

Ground Waters 

The Importance of Ground Waters — Origin and Occurrence of Ground 
Water — Movements of Ground Water — Springs — Artesian Condi- 
tions — The Underflow of Streams — Temperature of Ground Waters — 
The Qualities of Ground Water — Velocities and Quantities of 
Ground Water Flow — Wells — Literature 390 

CHAPTER XVI 

Stream Flow or Runoff 

Source of Runoff — Importance of the Study of Runoff — Occurrence of 
Runoff— Difficulties of the Problem— The Factors of Runoff— Pre- 
cipitation — Geographical Relation of Drainage Area — Topography 
and Geology of Drainage Area and Channel — Meteorological Condi- 
tions — Surface Conditions — The Character of the Storage on the 
Drainage Area — Artificial Use and Control of Streams — Conditions 
Favorable to Maximum Water Supply and Equalized Flow of 
Streams — Conditions Favorable to Minimum Runoff — Discussion of 
Extreme Conditions — Literature 432 

CHAPTER XVII . 

Variations in Runoff or Stream Discharge 

Importance of a Knowledge of the Variation in Stream Flow — Considera- 
tion of Public Water Supplies — Consideration of Supplies for Power 
Purposes — Consideration of Supplies for Irrigation — Consideration 
of Supplies for Other Uses — Physical Variables in Engineering Prob- 
lems — Measurement of Stream Flow — Difficulties in Stream Measure- 
ments — Runoff Data and Their Use — Variation in the Discharge of 
the Same Stream — Seasonal Variations in Streams — Rainfall and 
Runoff — The Lag of Stream Flow — The Retardation of Flood 
Waves — Effects of Storage on Runoff — Variation in Annual Rela- 
tions of Rainfall to Runoff — Approximating Rainfall-Runoff Re- 
lations — Percentage Estimates and Empirical Expressions — Varia- 
tions in Periodic Rainfall and Runoff Relations — Rafter's Curves of 
Periodic Rainfall Runoff Relations — Discordance in Rainfall-Run- 
off Relations — Literature 473 

CHAPTER XVIII 

Estimating Runoff 

Rational Methods of Estimating Runoff — Vermuele's Method — Justin's 
Method — Meyer Method — Basis of all Methods of Stream Flow 
Analysis — Runoff Problems — Runoff Problems with Large Storage 



Contents. xi 

(Flow Known — Runoff Problems with Moderate Storage (Flow 
Known) — Runoff Problems with Limited Storage (Flow Known) — 
Comparative Hydrographs with Large Storage (Flow Unknown) — 
Estimating Available Flow with Moderate Storage from Comparative 
Hydrographs — Literature 509 

CHAPTER XIX 

Floods and Flood Flows 

The Importance of Flood Studies — Changing Conditions and Flood Ef- 
fects — Great Floods and Flood Loses — Floods of the Lower Missis- 
sippi Valley — Floods of October, 1911, in Wisconsin — Other Flood 
Problems of the United States — The Cause of Floods — Time of Oc- 
currence — Relative Time of Occurrence of the Flood Crest in 
Rivers — The Rise, Duration and Recession of Floods — Flood Fre- 
quencies — Are Floods Increasing in Intensity and Duration — The 
Effect of Storage on Flood Heights — The Intensity of the Flood Run- 
off of Streams — Runoff from City Areas — Flood Runoff from Drain- 
age Districts — Flood Flows of Small Streams for Determining the 
Capacities of Railway Culverts — The Derivation or Selection of 
Formulas for Flood Flows — The Economics of Flood Protection 
Work — Literature 544 

CHAPTER XX 

The Application of Hydrology 

Fundamental Considerations — Applied Hydrology — Water Supply — Com- 
parative Sources of Water Supply — Factors for Water Supply In- 
vestigations — Irrigation — Irrigation Investigations — Water Power — 
Water Power Investigation — Internal Navigation — Investigation of 
Rivers, Canals and Harbors — The Sewerage of Cities — Factors of 
Sewerage Projects — Drainage — Land Drainage Investigation — Flood 
Protection — Flood Protection Investigation — Literature 597 



HYDROLOGY 



CHAPTER I 
INTRODUCTION 

i. Hydrology. — Hydrology treats of the laws of the occurrence and 
distribution of water over the earth's surface and within the geological 
strata, and of its sanitary, agricultural and commercial relations. Hy- 
drology in its broadest extent treats of the properties, laws and phe- 
nomena of water, of its physical, chemical and physiological relations, 
of its distribution and circulation throughout the habitable earth, and 
of the effect of this circulation on human lives and interests. This cir- 
culation is one of the important influences on the growth and develop- 
ment, or the changes and evolution from past through present to future 
forms and conditions in the earth's history, and has a most important 
bearing on the geographic extent of human activities. This circulation 
of water above, on and within the earth's crust, is as important and 
necessary in geological change and development as is the circulation of 
blood in the animal body or the circulation of sap to vegetable life. 
The latter are also dependent on water, of which they are largely com- 
posed. 

The phenomena and laws of all sciences are so interwoven that it 
has been said if a student has a complete knowledge of any *one 
he will have a complete knowledge of all. In a practical way, this 
idea is true to the extent that no science can be satisfactorily acquired 
without trespassing to a degree on many other sciences. So in the 
study of Hydrology we must, to an extent at least, seek information 
from Meteorology, Geography, Geology, Physiography, Agriculture, 
Forestry, and from the field of Plydraulic Engineering of which Hy- 
drology is the basic study. 

Hydrology discusses Hydro-Meteorology principally in relation to the 
occurrence, distribution, variation and disposal of rainfall and the runoff 
resulting therefrom in drought and in flood. It discusses the modifica- 
tions of the runoff caused by evaporation, topography, geology, tem- 
perature, and various other factors, and the variations in runoff as these 
factors vary in importance with the location or with the season. The 
great variations in the unit runoff under similar rainfall conditions but 



2 Introduction. 

different physical conditions, and under similar physical conditions but 
different rainfall conditions, are investigated, and the marked differ- 
ences which arise in different parts of the country with these differ- 
ences in conditions are discussed. The effects of storage, of cultiva- 
tion, of forestation and of other artificial physical modifications of the 
drainage area on the flow of streams, are also considered. 

Hydrology discusses Hydrography and Physiography in relation to 
the distribution and circulation of water over the earth's surface and the 
physical features that modify and influence such distribution and circu- 
tion. It discusses Hydro-Geology or the occurrence of water in the 
strata, and the laws of its occurrence and flow. This must presuppose 
or include a sufficient study of general Geology to give a comprehensive 
knowledge of the geological limitations which must be expected in 
hydrographic conditions and of the modifications due to geological 
changes. Water as a geological agent is discussed, and through such 
study a comprehension of the birth, growth, and the development of 
drainage systems and of rivers is attained. 

2. Prevalence of Law in all Natural Phenomena. — The study of 
Hydrology demonstrates the prevalence of law in the occurrence of all 
natural phenomena. 

Rainfall and its accompanying phenomena are proverbially incon- 
sistent, but Hydrology shows that there are limitations to such in- 
consistencies and that those limitations are quite as narrow and exact 
as those that must be considered in other engineering calculations 
which must be cared for by the "factor of safety" which is simply a 
"factor of inconsistency" in the qualities or occurrences of conditions 
with which the engineer always has to deal. 

The study of the development of rivers demonstrates that the ap- 
parently lawless and erratic action Of streams follows laws more or less 
distinct, which must be studied and comprehended before intelligent 
river conservancy becomes possible. 

The laws which control the circulation of water, on which its pres- 
ence or absence depend, and which modify and define its occurrence, 
attract attention and become of practical importance only as comprehen- 
sion of them permits of such adaptation to human affairs as will reduce 
or eliminate the injurious results which may otherwise happen during 
the occurring cycle, or will modify or effect a controlling influence 
which will adapt the occurrence to useful ends. 

3. Hydrological Influence on Early Settlement.— In primitive 
settlements, a profound knowledge of the detail of these laws and con- 



Hydrological Influence. 3 

ditions was of small importance. Normal conditions might render a 
locality unsuited to human use. The land might be too dry or too wet 
for agriculture and it would not be utilized. It might be subject to 
overflow from the tides or the river floods and remain unsettled, 
or if an attempt was made to utilize or to settle, it was abandoned 
on account of the rare occurrence of overflow, with more or less 
resulting loss when such overflow occurred. As land was abundant 
and of but little value, the individual had but to choose the location 
where the conditions were best suited to his purpose. 

The first settlements of a new country have normally and perma- 
nently occurred where water for drinking and other domestic uses was 
readily obtained ; where the normal rainfall, both in quantity and dis- 
tribution, was adequate for agriculture ; where the land was free from 
both drought and overflow ; where intercommunication among settle- 
ments was readily accomplished; where the location was accessible to 
navigation ; and where water power could be cheaply and readily de- 
veloped for primitive manufacturing. All of these elements have had 
an important influence in the development of every country. The 
earlier civilization developed along those seas, lakes and rivers where 
navigation was possible and where other elements were favorable to 
settlement. As the art of navigation developed so that the ocean could 
be crossed, the early settlements in new lands were along the shore 
where good harbors were found and where safe and ready ingress and 
egress were assured. 

Exploration and settlements followed the lines of navigation, and in 
America, the St. Lawrence River, the Great Lakes, and the Mississippi 
and Ohio Rivers afforded the lines of least resistance to the explorer 
and the settler. The settlement of New York spread up the Hudson 
and along the tributary rivers because of accessibility together with 
other favorable conditions, and the Delaware and James Rivers and 
Chesapeake Bay had a similar influence on the settlement of Pennsyl- 
vania, Maryland and Virginia. 

As other methods of transportation have developed, interior towns 
remote from navigable waterways have resulted, but the larger com- 
mercial communities are still situated where navigation as well as other 
means for transportation is available. 

4. Effect of Development on Importance of the Subject. — With 
the growth and development of the country, other hydrological factors 
exerted their influence. The water powers of Lowell and Holyoke 
were the prime cause of early industrial development at these places. 



4 Introduction. 

The same influences prevailed at numerous other locations in the East. 

The growth and concentration of population soon affect land values, 
and lands at first unutilized, on account of unfavorable hydrological 
conditions, gradually attract attention on account of their favorable lo- 
cation, and the questions of their reclamation, protection and utilization 
become of increasing consequence. A knowledge of the conditions that 
influence such lands gradually became important. The limits and ex- 
tent of the unfavorable conditions were examined and considered ; 
primitive attempts were made at their reclamation, often with destruc- 
tive results because the extreme conditions were unknown or unrecog- 
nized. Mankind gradually determined, by dearly acquired experience, 
the necessary extent and limits- of its powers. In some cases limiting 
values required only small effort ; in others the values were so great that 
extensive efforts and expense were warranted. 

In early reclamation work only crude efforts were possible for no 
knowledge or precedent existed, but as the development proceeded, the 
principles underlying successful work were made manifest, the in- 
fluences of conditions were determined, and the results of similar efforts 
were more readily and certainly assured. 

5. Basis of Present Engineering Practice. — Modern engineering 
endeavor is a development from the successful primitive efforts of 
the pioneer to better his condition, to make his home and prop- 
erty safe and accessible, and to secure and surround himself with 
the conveniences of civilization. From the experience of man in all 
climes and in all countries, have been established the principles on 
which the success of all engineering work depends. There is little 
essentially new or novel that is safe. The adoption or extension of 
past experience to new circumstances and conditions is the sound basis 
of successful work. Research alon'g new and original lines is but mod- 
erately productive and is seldom warranted in the solution of practical 
problems ; that 'is the function of the pioneer and the laboratory. The 
engineer with the great practical problem must call to his assistance 
the successful experience of the past, and must build along lines that 
do not admit the possibility of failure. It becomes therefore of funda- 
mental importance for the engineer first to recognize his problem, and 
all of the conditions and principles on which its solution depends, for 
the correct solution can depend on nothing less. 

6. Extent of Knowledge necessary for Successful Engineering 
Work. — In the application of any science to practical ends, it must be 
remembered that for real substantial success a knowledge of many 



Hydrological Influence. 5 

sciences and many facts is essential. Hydrologically, a water supply 
for any purpose may be satisfactory but it must be conserved and de- 
veloped by correct engineering design and construction to be an engi- 
neering success. Successful adaptation of sound engineering and con- 
struction may bring about satisfactory constructive results but still 
other things are needed for ultimate success. The legal aspect demands 
attention, the laws of the land must be observed, and the legal rights 
must be properly secured, but even more is needed. Business and 
financial conditions must also be considered. Can the proposition be 
made a commercial success? Will the use to which the project is to 
be put warrant the necessary financial outlay and produce a sufficient 
income to guarantee satisfactory results for the investment necessary 
for sound engineering work, under the laws of the land, and develop 
the hydrological resources to the extent required? 

For real success, each aspect is both independent and related to all 
others ; failure in one is failure in all. No one is the most important 
unless unrecognized, when its importance at once predominates. At 
least a limited understanding of hydrological principles is prerequisite 
to the successful solution of the simplest problems in hydraulic engi- 
neering. For the purpose of investigating the more complicated prob- 
lems, a more detailed knowledge of this science is essential, and the 
more extended the knowledge of this subject, the greater the assurance 
of the successful solution of all such problems. 

7. Casualties Due to Lack of Hydrological Knowledge. — Failures 
more or less serious have resulted in every branch of hydraulic engi- 
neering from the neglect to investigate the fundamental hydrological 
conditions and to appreciate the importance of fundamental hydrologi- 
ical knowledge. 

Water power installations have been built without sufficient 
knowledge of the regime of the stream on which their success depends, 
resulting in failures of greater or less consequence. In many cases the 
deficient supply has resulted in financial failure, the plant being perhaps 
continued in operation after liquidation by the original investors. In 
some cases even more marked failures have resulted. A water power 
plant, taking its supply from a mountain lake, was constructed a few 
years ago in Virginia. The lake was drained by the plant soon after 
operation began, and the dependable supply was found to be so small that 
the plant was abandoned. A dam and power plant were constructed 
within the decade on a Wisconsin river which proved to have a normal 
flow so deficient in quantity that the dam was abandoned and the 



6 Introduction. 

machinery moved to another location on a larger and more dependable 
stream. 

To the lack of proper geological knowledge and investigation must 
be attributed many expensive and serious failures. The failure of the 
dam at Austin, Texas, 1 was due to faulty foundation construction in 
the poor quality, open textured and faulted limestone. Similar con- 
ditions coupled with poor construction propably gave rise to the dis- 
astrous failure of the dam at Austin, Pennsylvania, in 191 i, 2 and of 
the Stoney River Dam in West Virginia. 3 

Cities have been founded in needlessly exposed positions and left 
unprotected, or so poorly protected as to be subject to great financial 
damage and loss of life from floods. Extensive damages have also 
been caused to farm and agricultural communities from similar causes. 
The Passaic flood of 1903 4 resulted from an unusually large rainfall 
and from rapidly melting snow. From October 8th to nth, 11.74 
inches of rain fell in the Passaic River basin. All storage on the basin 
was filled at the beginning of the storm, and in the resulting flood 
bridges were washed out, a large number of dams failed, many high- 
ways were destroyed, and much damage occurred to manufacturing 
plants and real estate. 

In the Kansas City flood 5 of the same year, a rainfall of five to ten 
inches occurred in sixteen days on the drainage area of the Kansas 
River, at a time when the river was above its normal flow and with 
the ground saturated. At Lecompton, the gage was twelve inches 
higher than any readings in twenty-two years. At Kansas City, the 
flood was fourteen feet above the danger line and two feet above the 
highest point reached by the previously highest recorded flood of June 
20, 1844. The damage that resulted was very great. 

The Johnstown flood, 6 which occurred in 1889, was probably one of 
the greatest disasters of the kind on record. This disaster was due to 
the insufficient provision of spillway. Continued rains saturated the 
soil and caused practically all of the water of a succeeding heavy storm 



1 Water Supply Paper No. 40, by T. U. Taylor. Eng. News, September 5, 
1901; Eng. News, April 12, 1900. 

2 Dam Failure at Austin, Pa. Eng. News, March 17, 1910. 

3 Break in Stoney River Dam. Eng. News, January 22, 1914. 

4 Passaic River Flood of 1903. New Jersey. U. S. G. S. Water Supply & 
Irrigation Paper No. 92, M. O. Leighton. 

5 Kansas City Flood of 1903. Destructive Floods of 1903, by E. C. Murphy. 
U. S. G. S. Water Supply and Irrigation Paper No. 96.' 

' 6 Johnstown, Pennsylvania, Flood of 1889. Eng. News, June 1, 8, 15 and 
22; July 13, and August 17, 1889. 



Casualties Due to Lack of Knowledge. 7 

to run off rapidly, raising the water in the reservoir and finally over- 
topping and destroying the earth fill dam, and releasing a great flood 
of water which descended on the unprotected cities and villages below 
with great loss of property and life. Over five thousand lives were lost 
in this flood, and the property damage amounted to many millions. 

The insufficient provision of capacity for passing flood waters caused 
the destruction of the reservoir dam at the Dells of the Black River in 
191 1. 7 While the spillway of the lower dam at Hatfield was undoubt- 
edly adequate for normal maximum floods, the sudden discharge of 
some 14,000 acre feet of water into the lower reservoir, resulted in the 
water overtopping the earth fill portion of the lower dam. Perhaps 
10,000 additional acre feet of storage were released from the lower res- 
ervoir, and the resulting flood destroyed the principal business district 
of the city of Black River Falls, Wisconsin, entailing a large loss of 
property, though fortunately no lives were lost. 

The great flood in the eastern United States in March, 1913. which 
caused a loss of perhaps four hundred lives and $100,000,000 in the 
Miami Valley alone, was due to an excessive rainstorm accompanied 
by other unfortunate physical conditions and so centered over certain 
drainage areas as to cause an unusual flood state. 8 

These floods demonstrate the lack of fundamental data in regard to 
the possible extremes of such occurrences, and emphasize the necessity 
for more extensive investigation and observation of both rainfall and 
stream flow, and the effect of other physical conditions on these occur- 
rences. 

The loss of more than six thousand lives and over $17,000,000 in 
property in the city of Galveston, on September 8, 1900, 9 due to a West 



1 Black River, Wisconsin, Flood of 1911. Eng. Record, October 14, 1911. 

s Wabash River Flood, March 21— April 2, 1913, by R. L. Sackett. Eng. 
News, April 24, 1913. 

Recent Flood at Columbus, Ohio, by Julian Griggs. Eng. News, April 10, 
1913; see also Eng. Rec. April 19, 1913. 

Flood Devastation at Dayton, Ohio. Eng. Rec. April 12, 1913. 

Flood of March-April, 1913, on the Ohio River and its Tributaries, by John 
C. Hoyt. Eng. News, April 10, 1913. 

The Ohio Valley Flood of March-April, 1913, by A. H. Horton and H. J. 
Jackson. U. S. G. S. Water Supply Paper No. 334. 

9 Galveston, Texas, Flood of 1900. The Encyclopedia Americana. Sci- 
entific American Compiling Department. 

The Lesson of Galveston, by W. J. McGee. National Geographic Maga- 
zine, Oct. 1900. 



8 Introduction. 

Indian hurricane which drove the water of the Gulf of Mexico over 
the city, was a serious lesson on the protection of cities from unusual 
conditions which are not, and perhaps cannot always be foreseen or ap- 
preciated. The occurrence of a similar storm in 1915, 10 and the result- 
ing casualties show that Galveston and other cities along the Gulf of 
Mexico are frequently subject to such contingencies and have not as 
yet taken the precautions necessary for their safety. 

In the last few years, failures in various irrigation projects, due 
often to inadequate water supplies, have been numerous. In few cases 
are the facts available, for those who have suffered from such mis- 
takes have usually preferred to bear these losses quietly and not make 
public the cause of such failures. Only in the case of the work of the 
United States Reclamation Service are facts of this kind available. 

The Hondo Project 11 of the United States Reclamation Service in 
New Mexico, was designed to take, its water supply from the Hondo 
River. The river has an intermittent flow only, but based upon a 
study of rainfall records, together with a consideration of the possible 
runoff due to topographical conditions, the construction was under- 
taken with the expectation of operating on stored flood waters. The 
construction was completed in 1906, but since that time the runoff has 
not been sufficient to allow the storage of enough water for practical 
use. 

In very many cases in the past, public water supply systems have been 
designed and constructed to utilize supplies of water which have later 
been found much too limited for the purpose for which they were in- 
tended, and expensive changes in the works have thus been made nec- 
essary ; or such works have been constructed in locations where the 
supplies have afterwards been found to be polluted and undesirable, 
with similar expensive results. Iri a certain city in Illinois, a pumping 
station was located near a spring which was developed by means of a 
large masonry well. When pumping began, the well was soon emp- 
tied and the inflow was so insufficient that the well and station were 
abandoned and a new station was constructed in an entirely different 
locality. In another case, in a city of considerable size, a well was con- 



10 Galveston's Sea Wall Checks Hurricane Devastation, by E. B. Van de 
Greyn. Eng. Rec. Aug. 28, 1915; see also Eng. News, Aug. 26, 1915, and 
Sept. 2, 1915. 

Effect of Galveston Storm on Sea-Wall and Causeway, by R. P. Babbitt. 
Eng. News Aug. 26, 1915. 

11 Hondo Project. House of Representatives. Document 1262 (1911). 3d 
Session 61st Congress. 



Variations in Phenomena. 9 

structed at a large expense into a gravel deposit which furnished a 
supply adequate in quantity but entirely unsatisfactory in quality. A 
limited investigation afterwards proved that the gravel stratum under- 
laid the thickly settled portion of the city and drained the vaults and 
cesspools of the unsewered area. Such examples were very numerous 
in the early days of the installation of water supplies, when limited 
knowledge and experience had not demonstrated the need of study 
and investigation. They are much too common even now when the 
experience of the past is available as a warning of the necessity of a full 
knowledge of these fundamental conditions. 

Great losses have been sustained, property ruined, and unsanitary 
conditions created by the overflow of storm water from sewers and 
drains of improper design. The records of almost every city will give 
examples of such occurrences. 

Unfortunately for the greatest success of future projects, mankind 
prefers to publish its successes and to conceal its failures, while fre- 
quently much more might be learned from the latter than from the 
former. 

Many of the unfortunate occurrences briefly described above have 
been due to the lack of investigation and of a thorough understanding 
and appreciation of the fundamental principles and knowledge of phe- 
nomena which it is the province of Hydrology to discuss. 

8. Variations in Hydrological Phenomena. — Many of the funda- 
mental phenomena which must be considered in the problems of Hy- 
drology are exceedingly variable in occurrence as regards quantity, in- 
tensity and time, much more so, in fact, than the ordinary observer 
would suspect. It is a common idea that, taking the season through, 
the average rainfall is not greatly different from year to year either in 
amount or distribution, yet the rainfall at Madison, Wisconsin, has 
varied from a minimum of 1349 inches in the year 1895 to a maximum 
of 52.93 inches in 1881, and the variation in monthly distribution is 
still more irregular. A better knowledge of these variations is, how- 
ever, now becoming common through the valuable work of the United 
States Weather Bureau. 

The casual observer is not apt to realize the great variations that 
occur in the flow of streams, concerning which he has no means of 
exact information. His conclusions in regard to stream flow are 
usually drawn from personal observation, and his observations on sub- 
jects in which he has little personal interest are inexact and hence tend 
to error. Extended and exact observations will show that stream flow 



1 Introduction. 

is subject to extreme variations both in drought and in flood, and the 
limits of these variations are even greater than those of the rainfall on 
which stream flow so largely depends. 

Floods similar to those of March, 1913, in Ohio and Indiana which 
surpass all previous records, give indications of the possibilities of ex- 
treme conditions which may occur beyond any which seem probable 
from the recorded data available. 

The maximum flood must result from the simultaneous occurrence 
of all conditions favorable to runoff, and it cannot be said, with the lim- 
ited records of such phenomena, that such simultaneous occurrence of 
favorable conditions has as yet been realized even in the most extreme 
recorded case. 

The uncertainty of many meteorological phenomena is proverbial. 
The great variation in the character of the seasons throughout a period of 
years is very marked. The irregularity in the occurrence of rain and 
snow, of storms and sunshine, is a matter of common observation. 
The observer is therefore naturally led to expect that other phenomena, 
dependent largely or partially on meteorological conditions, will be sub- 
ject to a similar variation, and be equally uncertain. On the other hand, 
a few casual observations in which these great variations are seen, 
might lead to the belief that meteorological phenomena follow no law, or 
at least follow laws so complicated and involved as to be hopelessly ob- 
scure. They might also lead the observer to the conclusion that no 
ascertainable relation exists between rainfall and stream flow, or be- 

i 

tween other interdependent hydrological phenomena. Accurate and 
continuous observations, however, show that while great variations ex- 
ist, they are limited in character and extent, and that the relations 
between the various factors of Hydrology and Meteorology, while com- 
plicated, are nevertheless fixed and by extended observation can be ren- 
dered sufficiently determinate to enable valuable deductions to be based 
on them. . It is most important that the engineer should realize both the 
great variations which occur in these phenomena and the limitations of 
such variations. 

The engineer is therefore frequently obliged to draw conclusions of 
greater or less importance, often from very inadequate data, as to the 
rainfall, the resulting ground water supply, runoff and their possible 
extremes from some given source or drainage area. In such cases, 
he may be obliged to estimate the probable and possible rainfall condi- 
tions from comparisons with other areas where such data, also fre- 
quently inadequate, are available, and which areas are similarly located 



Factors of Safety. 1 t 

geographically, topographically and meteorologically, and where, on 
'account of such similarity of location and conditions, similar inten- 
sity and magnitude of rainfall may reasonably be anticipated. 

It is readily demonstrable that local conditions are never exactly du- 
plicated and that any comparisons, between apparently similar locali- 
ties are subject to possible errors of considerable magnitude. Hence, 
estimates of rainfall and runoff, and the design of structures based on 
such comparisons, must for safety be made with these probable errors 
in mind and must include factors of safety proportional to the possible 
errors involved and the serious nature of possible casualties which 
might result from designs based on such erroneous data. 

In considering these problems it is important to recognize the fact 
that general principles frequently are subject to wide variations, and 
even to marked exceptions, especially when relating to the compli- 
cated subject of meteorology. It is highly essential therefore in as- 
suming that any general principle may or will obtain in a given lo- 
cality to secure sufficient data to demonstrate that all conditions are 
favorable to the probable prevalence of such principles and the prob- 
able force or intensity of the phenomena resulting thereunder. It 
must also be remembered that only limited conclusions should be 
drawn from limited observations. In many cases, conclusions based 
on data for single months or years would be entirely reversed if based 
on observations for other similar periods ; and both would be altered 
if based upon the average and extremes shown by long series of ob- 
servations. 

9. Factors of Safety in Engineering Work. — In all engineering 
work the contingencies to which any structures or plant will be sub- 
jected are of necessity more or less indeterminate, and the lack of 
exact information as to the actual conditions which will prevail, and 
which will influence the character and usefulness of a structure or 
plant during its life, require that, in order to provide for such unfore- 
seen conditions, a factor of safety shall be used and that the structure 
or plant shall be designed much stronger, larger or on different lines 
than the average condition would apparently make necessary. In the 
projects of hydraulic engineering, similar factors of safety must be ap- 
plied as in structural design. In hydraulic calculations, and in the cal- 
culations of the volume of flood and of low water flow, no large factors 
of safety are financially possible, and the supply or capacity of plants or 
works must be designed for essentially the results desired with only a 
small margin for safety. It will therefore be seen that, in carefully 



1 2 Introduction. 

made hydrological calculations, the probable inaccuracies are, in 
spite of the great variations before noted, no greater than in other 
engineering works, and, although there is much need for extended ob- 
servations and research, yet the applied science of Hydraulic Engineer- 
ing is, in exactness, fully abreast with other branches of engineering. 

10. Fundamental Laws. — Natural laws are always dependable and 
similar effects always result from similar causes. The difficulty of in- 
terpretation lies in the difficulty of differentiating and recognizing the 
causes to which the effect is due. Successful engineering work is the 
result of successful differentiation of the underlying facts and princi- 
ples, and the success of other work based on successful precedent lies 
in the ability to discern similarity of conditions, or to modify the de- 
tail so as to meet the new conditions involved. While the fundamental 
laws of Hydrology are unchanging, the factors which control their 
phenomena are so numerous that they result in wide variations in the 
relations of similar phenomena in different localities. As with all phy- 
sical phenomena, similar causes, when acting under similar conditions, 
produce similar results ; but the causes, and the varying conditions un- 
der which they act, must be carefully investigated and thoroughly un- 
derstood, in order that the result may be rightly anticipated. With the 
great variation in the circumstances of occurrence, it is therefore un- 
safe to apply data obtained from one locality, under one set of condi- 
tions, without modifications, to an entirely different locality' with rad- 
ically different conditions, and expect similar results. 

The laws of nature cannot be modified by human agencies, but such 
laws may be utilized under favorable conditions to accomplish results 
favorable to humanity. A knowledge of the conditions and of natural 
laws becomes of great irnportance when such adaptation becomes desir- 
able, and the degree of success assured in the desired adaptation corre- 
sponds with the extent of the knowledge possessed and applied. 

ii. Complexity of Influences. — Hydrological. problems are fre- 
quently difficult to solve on account of complexity of the influences 
involved. The geological, physiographical, topographical and mete- 
orological conditions vary to considerable extent, with every de- 
gree of latitude and longitude, and often with even less extended 
geographical differences. The meteorological conditions vary as 
greatly, and sometimes even more greatly with the change of sea- 
sons than with the change of locality. Each locality has therefore a 
combination of conditions more or less different and distinct from 
those of every other locality, however near or remote, and the laws 



Sources of Hydrological Knowledge. 1 3 

which control the occurrence of local phenomena are more or less 
modified by such local conditions. Hence, the local conditions must 
be investigated and determined before correct conclusions can be 
drawn concerning the dependable occurrence of hydrological pheno- 
mena. 

There are, however, geographical limits within which similar physio- 
graphical and climatic conditions prevail, and where hydrological con- 
ditions are so similar that conclusions, based on the data of one locality, 
can be applied, with only slight modifications, to other localities within 
such limits. If this were not the case, a science of hydrology would be 
impossible. The greatest difficulties encountered in the study of this sub- 
ject are these variations and the determination of their effect on phe- 
nomena. For accuracy and exact determination, sufficient data are not 
always available, hence the available data become still more valuable 
and the extension of these data becomes of great importance. 

12. Sources and Limitations of Hydrological Knowledge. — Our 
knowledge of hydrological phenomena is at the present day fragmentary 
and incomplete. While knowledge in the natural sciences has made 
great strides in the last two centuries, and our progress in many lines has 
been phenomenal, the value of a knowledge of the many hydrological 
data necessary for the satisfactory practice of hydraulic engineering has 
been but slowly realized. 

Rainfall observations have been made in a few isolated cases for 
perhaps 150 years or more, but anything like a systematic study of 
rainfall, even in the old countries of Europe, is of comparatively recent 
date. A few isolated rainfall observations, more or less continuous, 
were made in America in the iSth century. Several additional sta- 
tions were established and, although sometimes changed in location, 
have in this way been continuously maintained since early in the 19th 
century. By 1850, the number of stations at which such observations 
were made was considerably increased, and these stations were greatly 
extended when systematic work of this sort was taken up by the Sig- 
nal Service about 1870. The most of the precipitation stations have, 
however, been established since the organization of the Weather 
Bureau in 1891 ; but while these stations have already increased in 
number to 4,971, they are even now too limited to afford data for 
the satisfactory solution of many problems important to the hydraulic 
engineer. Where rainfall must be used as a basis for estimating the 
hydrological conditions for long periods in the future, it is evident that 
such data should be available for long periods in the past, and the com- 



1 4 Introduction. 

paratively recent establishment of present stations, therefore, makes it 
clear that our knowledge in this regard is much too limited. 

On the subject of streamflow the data are still more incomplete. 
The measurement of flowing water is more difficult than the measure- 
ment of rainfall, and in very few cases have reliable observations of 
the flow of any stream been continued for half a century. About 1893, 
the United States Geological Survey began to accumulate data and to 
make observations on the flow of streams, and the published reports 
of the Survey are the principal source of information from which such 
data can be obtained. Owing to financial limitations, the extent of 
these measurements and observations is far more restricted than those 
of rainfall, and the stream flow in many locations and many stream- 
flow conditions remain essentially unknown and are still to be inves- 
tigated. 

In this connection the stream gage height observations collected and 
made public by the Weather Bureau afford valuable data from which, by 
comparison, more limited observations can sometimes be extended. 

Geological data from which hydrological conditions of under- 
ground water sources may be studied, have been accumulated rapidly 
in the last twenty-five years and are found in the numerous volumes 
published by the United States Geological Survey and by the geological 
surveys of the various states. 

The development of all of these branches of knowledge goes hand 
in hand with civilization and has been extended as settlement has ex- 
tended and as the prospective demand of civilization has pushed the 
frontier of knowledge farther and farther into hitherto unknown re- 
gions. 

The work of the hydraulic engineer is frequently required to make 
settlement possible, hence in many cases hydrological problems arise 
in regions where such investigations have never been made or have 
only just begun. The difficulties that arise in such cases must be 
known and appreciated in order that the work of the engineer may be 
conducted on conservative lines and result in developments whose ac- 
complishments will assure the success and permanency of social domin- 
ion over the new lands. 

13. Determination of Hydrological Relations. — In considering the 
involved question of hydrology it is most important to disabuse the 
mind of personal bias and to leave it as free as possible to form conser- 
vative and logical conclusions from the best data available. 

It is a common experience that man}- men formulate an hypothesis 



Determination of Relations. 1 5 

and gather data to prove it instead of first collecting the data and form- 
ulating an hypothesis therefrom. With sufficient bias almost any con- 
clusion can be reached to the satisfaction of the prejudiced investi- 
gator. All correct hypotheses must rest upon either or both inductive 
and deductive reasoning, and to the extent that the hypothesis fulfills 
the requirements of both methods it may be regarded as correct. 

Inductive reasoning consists in establishing a general law on many 
observations in which a certain effect is found to follow a certain cause. 
This process depends fundamentally upon eliminating so far as possible 
other contributing causes so that the effect in question may correctly 
.be attributed to the one contributing cause. As the factors become 
complicated, the results of such investigations become uncertain and 
can finally be demonstrated in a satisfactory manner, if at all, only by 
extended investigations and when the main cause is so predominating 
as to produce an effect in spite of other complicating factors. If, for 
example, it is desired to investigate the relations of annual evaporation 
from soil to annual rainfall (see Sec. 74), the results of a long series 
of observations, under conditions where other factors are as similar 
as possible, are platted with annual evaporation and annual rainfall 
as ordinates and abscissas respectively and the relations of these platted 
points are observed. (See Fig. 85, page 140). If the annual evapora- 
tion were essentially constant, regardless of the variation in annual 
rainfall, the observations would fall approximately on a horizontal 
line representing the mean annual evaporation. If, however, the an- 
nual evaporation increases with rainfall, as seems to be true, such fact 
will be indicated by the relative location of the points on the drawing ; 
and if the centers of gravity of the higher and lower groups of points 
respectively be determined, the location of such centers of gravity will 
indicate the direction of an inclined line which will more clearly rep- 
resent the mean annual relations of evaporation and rainfall. It will 
"be noted from Fig. 85 that for the two years in which rainfall was 
23.5 inches, the evaporation was 13.9 and 22.2 inches respectively. 
This would seem to indicate that the general hypothesis is incorrect. 
The departures of the various observations from the line of mean an- 
nual relations so established do not, however, indicate that the hypo- 
thesis is incorrect but they show that other factors are present which 
frequently so influence and obscure the relations of the two factors 
■considered that they may frequently overcome the general relations 
established. 

The relations of various factors in different phenomena may be in- 



1 6 Introduction. 

vestigated in a similar manner and experimental curves 12 established 
showing the relations found which may be reduced to formulas more 
or less broadly applicable. The ultimate truth of any hypothesis ad- 
vanced or of any formula proposed is confirmed when it is always 
found to apply to extended series of observations in the investigation 
of which it can be consistently employed. Relations so determined are 
both quantitative and qualitative and are therefore of the greatest use 
to the engineer as a basis for his conclusions. 

Deductive reasoning is based on well established fundamental prin- 
ciples that are known to obtain from previous experiences. From 
these fundamental principles a certain effect is clearly deduced as a 
consequence of a certain cause. From such deduction, coupled per- 
haps with other fundamental principles, other results are found neces- 
sarily to obtain and the same process is extended until the ultimate 
conclusions are reached. Here too the process of reasoning is com- 
plicated by involved conditions which frequently lead to serious error 
unless every step is closely scrutinized. Deductive logic is the basis 
of all sciences and its methods are rigidly exact if correctly used. In 
hydrological problems the results of deductive reasoning are usually 
qualitative rather than quantitative. 

In complicated problems of hydrology, the investigator needs the 
aid of all possible logical methods, and even where every method of 
logic is applied it is frequently found that on account of limited or in- 
correct data and lack of knowledge of certain fundamental principles 
involved, the relations sought can by no means be definitely established. 
Indications may lead to certain general conclusions, and while such 
conclusions may be inexact they may be the best possible from the ex- 
perience and knowledge at hand. Under such conditions any con- 
clusions must be regarded as tentative only, utilized with caution, and 
final conclusions must be withheld pending broader observation and 
more extended experience. 



i- See Empirical Formulas, by Prof. T. R. Runney. John Wiley & Sons, 
Inc. 1917. 

Practical Mathematics, by Prof. F. M. Saxeby. Longman-Green Co., 1905, 
Chap. VIII. 

Methods for Determining the Equation of Experimental Curves, by H. S. 
Landsdorf. Jour. Asso. Eng. Soc. Vol. 32, p. 325, 1904. 

Determination of Experimental Equations, by L. F. Harza. Wisconsin- 
Engineer, Dec, 190S. 



Danger of General Conclusions. 1 7 

14. Danger of General Conclusions. — In considering many of the 
simpler phenomena, the relations between cause and effect are so direct 
as to be readily understood and appreciated. The very simplicity of 
such relation is apt to be misleading when more complex phenomena 
are under investigation and, in consequence, undue weight is often 
given to some single influence that may be only one of many which 
modify or control the results under consideration. 

By complex phenomena are meant those in which the effect is modi- 
fied by numerous causes, each influencing the ultimate result not only in 
accordance with its own character and intensity, but also in accordance 
with the relative character and intensity of other co-ordinate influences. 
The effect in such cases may be regarded as the resultant of numerous 
factors, and the weight, importance and effect of each must be care- 
fully differentiated in order that its relative importance may be rightly 
understood and clearly appreciated. Most meteorological and climatic 
problems are of this class ; and many such problems are so involved in 
character, the factors that modify their occurrence are so complicated 
and so irregular, and they are often so modified by unappreciated, and 
perhaps by unknown causes, as to make their occurrence appear to the 
limited vision of the casual observer as devoid of law and beyond the 
possible knowledge of mankind. 

The first common error in the consideration of such problems is the 
assumption of a simplicity of the relations between cause and effect 
that is not warranted by fact. The second common error is the as- 
sumption that when a certain cause is operative under one set of condi- 
tions that it is operative to a similar degree under all other conditions. 
The third common error is due to the confusion of cause and effect, 
or in attributing the cause to the effect instead of the true relation of 
the effect to the real cause. 

The rapid advance in fundamental science and the development of 
many startling and hitherto almost unknown phenomena, applicable 
perhaps to new commercial development have, in cases, given the un- 
wary a basis for a belief in possibilities not yet developed, and in many 
cases, most improbable. This readiness of the public to anticipate 
great advancement in scientific achievements has been utilized by psuedo 
scientists to advance immature ideas as though they were established 
principles and to make unsubstantiated claims for personal or class 
reasons. In many cases such claims are advanced in good faith, based 
on only a partial examination of all the data of the problem. 

There are those who, even in the face of the vast number of almost 
Hydrology — 2 



1 8 Introduction. 

unstudied influences that control the weather conditions and the al- 
most insignificant data yet available, still believe in the present possi- 
bilities of long advanced weather predictions. 

The foresters and their friends see in the planting of trees, which is 
only one of manifold active influences, the solution of flood troubles 
and low water conditions. Others, reasoning from cause to effect, 
assert material increase in precipitation to be due to forests or irrigation ; 
and in manifold other lines, marked influences on extended phenomena 
are declared due to limited developments in one of many controlling 
factors. The engineer must not be misled by psuedo-scientific argu- 
ment. His analysis must be complete, his conclusions conservative and 
limited to the case at hand to which his data apply ; and even in ex- 
tending his personal experience from one field to another, he must keep 
in mind the new factors which may always be present and which must 
modify the conclusions which, under other conditions, he has known 
to be definitely established. 

Experience is a most important teacher, and much of the knowledge 
of greatest value in practical life is acquired only by this means. 
Where certain local conditions in various parts of the world or even in 
the same country differ greatly, conclusions based on the conditions of 
one locality must be applied to any other locality only with great care. 
For example the ice conditions of the Arctic and Antarctic regions give 
rise to climate and physical conditions which are not fairly comparable 
with temperate regions where ice is a seasonal phenomenon. Rainfall 
in one country, or even in a part of the same country, may be well dis- 
tributed for agricultural purposes, while in another location even a 
greater annual rainfall may be so distributed as to occasion a serious 
shortage of moisture during the seasons of plant growth. Again, 
geological and topographical conditions may make certain phenomena 
largely local both in quality and intensity, and produce results from such 
causes which will be greatly different or absent altogether under radi- 
cally different conditions. 

The relation of the rainfall to the amount and distribution of water 
flowing from any given drainage area is a complicated problem. The 
flow from an area is so directly dependent on the rainfall thereon that 
it seems some simple and constant relation should be ascertainable 
between the quantities of each. A brief investigation, however, shows 
that the modifying conditions are manifold and that the relative im- 
portance of each influence varies even more widely than the apparent 
range in the conditions. These influences are so numerous, and their 



Study of Hydrology. 1 9 

modifying effect on one another is so direct and important, that no 
general and constant relation exists between any one influence and the 
ultimate results. These facts have led to many misinterpretations and 
erroneous conclusions in the attempt to establish simple relations which 
from the nature of the case cannot exist. Many serious errors and 
resultant losses have been occasioned by the adoption of general con- 
clusions, based perhaps on an accurate analysis of one series of local 
conditions, but applied under other conditions where such conclusions- 
were not at all applicable. 

Conclusions from hydrological data must therefore be adopted with 
caution and should generally be confined to limited localities until 
experience warrants their extension to wider fields. 

15. Purpose of the Study of Hydrology. — The purpose of the study 
of Hydrology is primarily to acquire a knowledge of the extent and 
limits of the variations in hydrological phenomena, to ascertain the 
effects on such phenomena of the various physical conditions that ob- 
tain in any locality, and to investigate the geographical limitations within 
which the observed phenomena may be applied with greater or less 
modifications, also to establish as far as may be, such laws as will aid 
in the determination of the effects to be expected from other physical 
conditions which are found to obtain. For these purposes the study 
of Hydrology must include : 

First: The study of the general physiographical, geological and topo- 
graphical features of the earth, the factors that have produced and are 
now modifying such features, and their general hydrological relations. 

Second: The study in a more specific way of these physical condi- 
tions and factors in relation to the area of the country to which the 
practice of the engineer will be largely confined. 

Third: The study in still greater detail of the hydrology of certain 
localities where certain important laws or relations are found to be 
best exemplified. 

It is the further purpose of this text to emphasize more particularly 
those lines of hydrological study that are most important, and the nec- 
essary and desirable direction in which hydrological investigation and 
study should be extended. 

16. Study of Hydrological Literature. — Only a brief examination 
of the subject of Hydrology is necessary in order to appreciate the 
complexity of the subject and the extent of the field which must be ex- 
amined in order to secure the data to demonstrate the principles on 
which its application must rest. It at once becomes apparent that a 



20 Introduction. 

single treatise can do little more than point out the main underlying 
principles, and illustrate the same with a few general data which will 
indicate the direction and extent of the variation which must be antici- 
pated and the character of the further investigations needed in the 
solution of local problems. In the actual application of these princi- 
ples to practical work it is evident that they must be studied in the 
light of a detailed knowledge of local circumstances and conditions,, 
and that in every case those principles which are to be directly applied 
must be considered in much greater detail than can possibly be done in 
any single volume. It is not the hope of the author to offer a complete 
treatise on this subject to the student or engineer, but only to point out 
the general relations that have been established, the general principles 
that are involved, and the necessity that exists for further research 
and study before any concrete problems can be solved even approxi- 
mately. 

There is now in existence an extensive literature on various hy- 
drological subjects, otherwise this book could not be written. While 
confining these pages to a brief consideration of the fundamental prin- 
ciples on which Hydrology rests it has also been the purpose of the 
author to point out, so far as possible, the source of the data which 
have been utilized and the further sources of information which are 
available for a more complete study of the various phases of the sub- 
ject. In the solution of any concrete problem, the various publications 
which are noted in the list of literature following each chapter must 
be consulted in detail, and conclusions offered by the author should be 
accepted only so far as the data on which they are based seem to war- 
rant. As noted in Section 14, general conclusions must be accepted 
with care and applied only when fully substantiated by all the local 
data which are available. Only by the greatest care can the correct 
conclusions be drawn for any specific hydrological problem, and even 
conclusions so reached are subject to various uncertainties. The broad- 
est investigation and study are essential to a sound conception of the 
various problems which the engineer must meet. 

17. References to Failures in Hydraulic Engineering Works. — 
The student or reader should study one or more of the following 
failures, and prepare a statement concerning the cause and results of 
the failure, and the nature of the information which should have been 
acquired or investigation which should have been made in order to 
have assured success. 



Failures. 2 1 

1. Johnstown, Pa. The Johnstown Disaster. Eng. News, June 1, 8, 15, 22; 

July 13; Aug. 17, 1SS9. 

2. Austin, Texas. Failure of Masonry Dam. Eng. News, Feb. 22; April 12, 

19; May 10; June 21, 1900; Eng. Rec. April 14, 21; May 2G; June 9, 
30; Juiy 28, 1900. 

3. Fishkill, New York. The Failure of the Melzingah Dams of the Fishkill 

and Matteawan Water Company. Eng. News, July 22, 1897. 

4. St. Anthony Falls, Minn. Effects of Mississippi River Floods on the New 

St. Anthony Falls Dam at Minneapolis. Eng. News, May 13, 1897 

5. Minneapolis, Minn. Failure of a Minneapolis Dam by Ice Pressure. Eng. 

Rec. May 13, 1899; Eng. News, May 11, 1899. 

6. Collingswood, N. J. Standpipe Failure. Eng. Rec. Jan. 20, 1900. 

7. Elgin, 111. The Failure of the Standpipe. Eng. News, May 3, 1900. 

8. Providence, R. 1. The Failure of Two Earth Dams. Eng. News, March 21, 

1901. 
y. Jeanette, Pa. The Failure of the Oakford Park and Fort Pitt Dams. 
Eng. News, July 23, 1903; Proc. Engrs. Club of Phila., July, 1904. 

10. Cobourg, Ontario. Damage by Ice to a Standpipe. Eng. News, Aug. 18, 

1904. 

11. Phoenix, Ariz. Construction, Repairs and Subsequent Partial Destruc- 

tion of the Arizona Canal Dam. Eng. News, April 27, 1905. 

12. Hauser Lake, Montana. The Break in the Hauser Lake Dam. Eng. News, 

Apr. 30, 1908. 

13. Fergus Falls, Minn. The Failure of the City Dam. Eng. News, Oct. 14, 

Nov. 3, 1909. 

14. Pittsfield, Mass. The Undermining of a Reinforced Concrete Dam. Eng. 

News, April 1, 1909. 

15. Utah. The Failure of an Irrigation Dam. Eng. Rec. Sept. 18, 1909. 

16. New Mexico. The Failure of the Bluewater Dam. Eng. News, Sept. 30, 

1909. 

17. Necaxa, Mexico. The Slide in the Necaxa Hydraulic Fill Dam. Eng. 

News, July 15, 1909; Eng. Rec. July 3, 1909. 

18. New Mexico. Partial Failure thru Undermining of the Zuni Dam. Eng. 

News, Dec. 2, 1909. 

19. Austin, Pa. Partial Failure of a Concrete Dam. Eng. News, Mar. 17, 

1910. 

20. Erindale, Ontario. Failure of an Earth Dam with Concrete Core Wall. 

Eng. News, April 14, 1910. 

21. Austin, Pa. The Failure of a Concrete Dam. Eng. News, Oct. 5, 1911; 

Eng. Rec. Oct. 7, 14, 1911; Proc. Engr's Club of Phila., Jan. 1912. 

22. Black River Falls, Wis. Failure of the Dells and Hatfield Dams and the 

Devastation of Black River Falls. Eng. Rec. Oct. 14, 21, 1911; Eng. 
News, Oct. 19, 1911. 

23. Mineville, N. Y. Failure of the Dalton Concrete Corewall Dam. Eng. 

News, May 9, 1912. 

24. Ohio River. Failure of Dam No. 26. Eng. News, Aug. 22, 1912. 



22 Introduction. 

25. Ontario, Canada. The Failure of the Dam of the Erindale Power Com- 

pany. Eng. Rec, April 27, 1912. 

26. Winston, N. C. The Failure and Repair of the Winston .Water Works 

Dam. Eng. News, April 11, 1912. 

27. Port Angeles, Wash. Washout of Base of Port Angeles Dam. Eng. Rec. 

Nov. 30, 1912. 

28. Dam and Embankment Failures in 1912. Eng. Rec. Apr. 19, 1913. 

29. Stony River, W. Va. Break in the Stony River Dam. Eng. News, Jan. 22, 

1914; Eng. Rec, Jan. 24, 1914; Jour. Engr's Soc. of Penn., Apr. 1914. 
The Reconstruction of the Stony River Dam. F. W. Scheidenhelm. 
Trans. Am. Soc. C. E., Vol. 81, 1917, p. 907. 

30. Tullahoma, Tenn. Failure and Reconstruction of a Small Dam. Eng. & 

Con., Nov. 11, 1914. 

31. California. ' Wreck of the Otay Rock-Fill Dam. Eng. Rec. Feb. 12, 1916. 

LITERATURE 

Manual of Hydrology, Nathaniel Beardmore. Waterlow & Sons, London, 1862. 

Hydrology of New York State, George W. Rafter, Bulletin No. 85, New York 
State Museum, 1905. 

Hydrography of the American Isthmus, Arthur P. Davis. United States Sen- 
ate Document No. 124, 57th Congress, 2d Session, 22d Ann. Rept. U. S. G. S., 
1900-01, pt. IV, p. 513. 

Hydrology of the Panama Canal, Caleb M. Saville. Trans. Am. Soc. C. E., 
Vol. 76, 1913, p. 871. 

Hydrography of Nicaragua, A. P. Davis, 20th Ann. Rept. U. C. G. S., 1898-9, 
pt. IV, p. 569. 

Elements of Hydrology, A. F. Meyer. John Wiley & Sons, New York, 1917. 



CHAPTER II 
WATER— ITS OCCURRENCE, UTILIZATION AND CONTROL 

18. Importance of Hydrological Conditions. — The conditions of 
the occurrence of water have an important influence on the develop- 
ment of every country. A closer analysis will show that the occur- 
rence and conditions of waters have even a more important influence 
than has previously been indicated. 

Water is and always has been one of the most important, if not the 
most important, of the agencies of topographical and geological change. 
To a greater or less degree it dissolves almost every form of mineral 
matter from the strata, which action is accelerated by the chemical 
activity of matter held in solution and by increased temperatures. Its 
expansion as it changes to ice by reason of low temperatures is a power- 
ful mechanical agency of disintegration. Its erosive effect in its flow 
from the mountains to the sea, aided by the detritus carried with it, has 
been a most potent agent in topographical development, and the dep- 
osition of materials transported to lakes and seas has been a most im- 
portant agent in geological growth. 

Without water organic life cannot exist. It is therefore one of the 
prime necessities of all organic life, and it is the largest constituent of 
all animal and vegetable matter. Its action as a solvent is here again 
a most important property in both animal and vegetable physiological 
processes. About two-thirds of the average human food is liquid. 
The average adult requires about 4^ pounds of simple liquid each 
day, with about 2]/ 2 pounds of solid food, which is about half liquid, 
intimately commingled with solid matter. Nutriment and oxygen are 
taken up and distributed to the various tissues of the animal body by 
the agency of the blood, which, is ninety per cent, water, and which 
also removes the waste products from the system. Vegetation is 
equally dependent upon water for the solution of food, its distribution 
to the vegetable tissue, and the removal of waste. 

Water is not only necessary for the existence of life, but its occur- 
rence and condition have a marked effect on health. A super-abund- 
ance may destroy or be seriously detrimental to both plants and ani- 
mals, and its character as influenced by the matter held in solution or 
carried in suspension may also have a serious effect on health. Water 



24 Water — Its Occurrence, Utilization and Control. 

draining from settled regions often receives and transports organisms 
which are prejudicial to the health of man if the water so polluted is 




Fig. 1. — Forest in the Olympic Foot Hills near Port Angeles, Washington. 
Annual Rainfall ahout 40 Inches (see page 25). 




Fig. 2. — Buckhorn Prairie Desert in Central Utah. Sage Brush in Fore- 
ground. Annual Rainfall about 12 Inches (see page 25). 

utilized for dietetic purposes. Water on account of its high solvent and 
transporting qualities, is constantly removing matter from the drainage 
area on which it falls and transporting it to other regions where it may 



Importance of Hydrological Conditions. 25 

be either beneficial or detrimental. In some irrigated regions the in- 
troduction of water has made possible successful agriculture, but a too 
lavish use has frequently brought alkalies to the surface to the detri- 
ment of plant life, or has turned the desert into a swamp on which agri- 
cultural products can no longer be grown. 

For successful agriculture, about 24 inches of annual rainfall, prop- 
erly distributed through the season, seems to be essential unless an 
artificial supply of water is provided. About 15 inches of rainfall 
per year is required for vegetation, and the remainder of the rain- 
fall is dissipated in other ways. For intensive cultivation, an addi- 
tional supply can be used to advantage. Where less than 24 inches of 
rainfall is available irrigation becomes desirable, and with a considerable 
decrease becomes highly essential (see Figs. 1 and 2, page 24). 

Water has always afforded an important means for transportation. 
For foreign commerce and for domestic commerce between points on 
the coasts and between points on the Great Lakes, navigation offers 
the most economical method of transportation of bulky materials. In 
the early development of modern civilization and prior to the evolu- 
tion of railways, river navigation was highly important. In undevel- 
oped countries, internal navigation is still the most important means of 
transportation (see Figs. 3 and 4, page 26). Even with railways 
well developed^ river navigation may be found more economical than 
transportation by rail where a permanent market requires the constant 
movement ot a large amount of bulky freight between river points. 
Under some conditions, artificial waterways or canals have been found 
desirable and economical, but they have become less important with 
the development of railway transportation. Canals for large vessels 
are feasible only when limited i 1 

First: To comparatively short connections between large and important bod- 
ies of water between which large traffic would naturally exist except for 
rapids or other natural barriers, as in the case of the Sault Ste. Marie 
Canal between Lake Superior and Lake Huron. 

Second: To comparatively short canals which save a very great sailing dis- 
tance, as in the cases of the Suez and Panama Canals. 

Third: To short canals connecting the sea with large commercial centers, as 
in the case of tb,e Manchester, England ship canal. 

The competition of long lines of canals with rail transportation is 
however no longer feasible under modern commercial conditions. 



1 Preliminary Report of U. S. National Waterway Commission, (Washing- 
ton, 1910), p. 13. 



26 Water — Its Occurrence, Utilization and Control. 




'<!.C 






! 



Fig. 3. — Boats at Gang Yuen, China. Transferring Salt on the Grand Canal 
(see page 25). (S. T. Suen.) 




Fig. 4. — Boats on the Grand Canal near Tsingkiangpu, China (see page 25). 

Transportation by means of navigation canals and rivers has lost the 
relative importance which it attained in the early history of commer- 
cial development. 

Water is also important as a source of power. It was of the highest 
importance in the earlier days of the development of our civilization 



Importance of Hydrological Conditions. 



27 




Fig. 5. — Washout around End of Marathon Dam, Rothschild, Wisconsin. 
Flood of October, 1911 (see page 28). 




Fig. 6.— Bridge Piers of Big Four Railroad near Miamisburg, Ohio. Under- 
mined and Part of Bridge Destroyed by Flood of 1913 (see page 28). 

prior to the evolution of the steam engine, and frequently was one of 
the most important factors in determining the location of manufactur- 
ing industries. With the development of the steam engine, the advan- 



28 Water — Its Occurrence, Utilization and Control. 

tage of a location near large centers of population or near lines of 
transportation overcame differences in the cost of steam and water 
power and the value of water power began to decrease. The develop- 
ment of large industries also rendered the small water powers of little 
value, and many which were developed and utilized at an early date 
were later abandoned. In late years electrical transmission and the 
use of electric current for light have given a new impetus to the develop- 
ment of water powers and made available at manufacturing centers 
many powers which could not previously be used to advantage (see 
Frontispiece). 

Water in certain phases of its occurrence becomes a serious menace 
to life and property. Surface waters under flood conditions and 
through the same characteristics that are productive of topographical 
and geological changes, endanger engineering structures constructed 
in their path, and through the destruction of such structures and on 
account of unusual volume and consequent height and velocity, im- 
peril human life and property during such periods (see Figs. 5 and 6, 
page 27). 

ig. The Occurrence of Water. — In a relative sense, the irregularity 
of the earth's crust is slight; the maximum elevation of the highest 
land is about 5.5 miles above sea level, and the greatest depth of the 
ocean is about 6 miles. The maximum variation in elevation, therefore, 
is only 14/100 of one per cent, of the earth's diameter, which is suffi- 
cient however, to raise somewhat more than a quarter of the earth's 
crust above the ocean. 

The exact relations of the area of land and water are not definitely 
known, as the Polar regions have not yet been fully explored. 

The total area of the globe is about 197,000,000 square miles. Of 
this the land occupies somewhat more than 50,000,000 square miles. 
About six-sevenths of the land area is situated in the northern hemis- 
phere of which it occupies about one-half of the total area, while in 
the southern hemisphere only about one-fifteenth of the area is land. 

Besides its occurrence in oceans, seas and the many inlets to the 
land connected therewith, water is found in various depressions in the 
earth's surface above sea level, where it collects and forms lakes, often 
of considerable extent, frequently connected by overflow channels with 
the sea to which the surplus waters flow. Occasionally, however, 
these lakes and island seas have no outlets because the waters collected 
are not sufficient in quantity to raise the surface of the lakes to the 
height necessary for overflow. 



Occurrence of Water. 



29 









Fig. 7. — Swamp in Southeastern Missouri. Little River Drainage District. 
Annual Rainfall about 45 Inches. (W. A. O'Brien). 




Fig. 8. — The Everglades of Florida. Annual Rainfall about 55 Inches. 
(Leonard Metcalf). 

In many cases the depressions are so shallow that aquatic vegetation 
occupies much of the area- and such bodies of water are classified as 
swamps and marshes (see Figs, y and 8). 

In many other cases, the depressions in the surface of the earth are 
elongated troughs in which water gathers as rivers and streams, and 



30 Water — Its Occurrence, Utilization and Control. 

through which, it flows from the higher lands to the lakes and to the 
oceans. In the extreme north and south are found great fields of 
snow and ice which are, from the limited view of human life, perpetual 
and which annually extend their areas far into the temperate zones dur- 
ing the winter season, withdrawing toward the poles with the advent of 
summer. 

Many of the geological strata, such as the sands, gravels and sand- 
stones, are highly pervious. The limestones are occasionally caver- 
nous, and most of the harder non-porous rocks are cracked and As- 
sured, frequently for many feet below the surface. Into the cracks, 
fissures and caverns and into the structure of the pervious deposits, 
the surface waters sink by gravity and slowly flow toward lower lev- 
els, when there are outlets at such levels as permit the water to dis- 
charge into the streams, lakes or oceans. Otherwise these rocks be- 
come and remain filled until some opportunity of discharge occurs. 
Such waters are classed as phreatic or subterranean waters and give 
rise to geysers, springs and artesian wells, and to deep and shallow 
non-flowing wells. 

The source of most phreatic waters and of all the waters of lakes, 
swamps, marshes, rivers and streams, is the rain or snow which falls 
in various quantities and at various times and seasons on the drainage 
areas from which such waters flow. 

20. Circulation. — The waters of the earth are always in motion, 
and circulate in various systems more or less separate and distinct. 
The waters of the oceans have a circulation produced by difference of 
temperature, by the rotation and revolution of the earth with respect 
to the sun and moon and the relative attraction of these bodies, and 
by the motion of the earth's atmosphere. These various influences re- 
sult in currents, tides and waves. Atmospheric movements, tempera- 
ture changes and other physical conditions give rise to evaporation, 
transportation and precipitation. The water precipitated on the land 
as rain, snow, dew or fog is again partly evaporated and part enters 
the water courses or seeps into permeable portions of the land sur- 
face and again seeks to return to the sea by virtue of gravity. It is in 
consequence of these systems of circulation of the hydrosphere that 
life on the globe is rendered possible, that the utilization of water for 
human betterment becomes feasible and that, on the other hand its oc- 
currence is often inimical to the interests of mankind. 



Circulation. 3 1 

The causes of the circulation of water on the earth's surface may 
'be more systematically reviewed as follows : 

First. — The waters of the ocean, heated at the tropics and cooled at 
the poles, have a motion toward the poles at the surface, and from the 
poles in the lower portions of the sea. 

Second. — The difference in velocity of rotation between equatorial 
and polar regions affects the flowing waters and gives the warm sur- 
face currents an easterly direction against the westerly continental 
shores. These currents are modified by continents, continental irreg- 
ularities, islands, and the larger rivers. 

Third. — The attraction of the sun and moon on the ocean and other 
large bodies of water produces the tides which follow the lunar revo- 
lution until they break on the eastern continental shores and then flow 
"back, vibrating synchronously with the lunar revolutions. 

Fourth. — The friction of atmospheric currents on the water pro- 
duces waves which at times of storm break with great force on ex- 
posed portions of the land. 

Fifth. — A constant evaporation goes on from all water surfaces. 
This is increased : a. By increased temperature, b. By the removal of 
vapor by movement of atmospheric currents. The vapor so formed 
rises into the upper atmosphere which when cooled becomes super-sat- 
urated and the moisture is precipitated as rain or snow. 

Sixth. — The rainfall and melted snow follow various courses : a. A 
portion is re-evaporated and passes into the atmosphere, b. A por- 
tion is utilized in plant growth or in plant transpiration which again 
reaches the atmosphere, c. A portion seeps into the strata, and follow- 
ing their dip, finds its way ultimately into the rivers and seas. d. A por- 
tion flows over the surface into the water courses and thence to the sea. 

Seventh. — In the polar regions and in high mountain altitudes, pre- 
cipitation takes place as snow and the temperatures are- so low that 
melting occurs in a comparatively small degree or not at all. The re- 
sulting vast accumulations of snow exert a pressure sufficient to form 
ice masses in their lower portions, which, from the super-imposed 
weight, are pressed outward until their glacial terminations either melt 
in the lower altitudes or reach the sea and are melted or broken off as 
ice bergs. 

The action of all these various factors which control the circulation 
■of water on the earth is modified by the local physical and meteorologi- 
cal conditions. 



32 Water — Its Occurrence, Utilization and Control. 

21. The Cleansing and Transporting Work of Water. — Water 
has been termed a "universal scavenger." As it condenses in clouds 
and is precipitated as rain, it cleanses the atmosphere of suspended 
mailer, organic or inorganic dusl and germ life, sufficiently lighl to be 
carried into the atmosphere by wind currents and which are found at 
all heights. After a long dry period, (lie rain that falls over a large 
city is highly polluted, while in the country districts, far from the 
smoke and dust of cities, the rainfall is more nearly pure. Rainwater 
therefore reaches the earth in a more or less impure state, and the 
earlier rainfall is commonly mosl greatly polluted by such impurities^ 
After it reaches the earth, it continues its cleansing action. It dis- 
solves some of the soluble matter with which it comes in contact, and 
lakes it]) and transports materials which it does not dissolve. The 
amounl and character of the dissolved and transported material de- 
pend Upon the character of the material with which the water comes 
in contact, the duration of the contact, and the volume and velocity of 
flow. If it falls on indurated areas, which are only slightly soluble, 
and cannot be eroded easily, it Hows away "soft" and clear. Such 

water may be comparatively pure and free from sediment. Falling 

on disintegrated strata or areas covered by glacial drift, the water 
frequently becomes more highly impregnated with mineral salts and is 
known as "hard water." In rapidly flowing streams the waters are 
frequently turbid, especially during the high velocities of Hood Hows. 
When waters seep into the strata, on account of longer and closer 
contact, they take into solution even greater amounts of salts than are 
found in the surface waters, and the character of such dissolved ma- 
terials depends on the nature of the deposits through which they How. 
They sometimes become highly saturated with mineral matter which 
is increased in quantity by the agency of dissolved gases, principally 
carbon dioxide (C0 2 ), and such waters when they reach the air 
through fissures or bore holes as springs or wells, frequently lose the 
dissolved gases and deposit the surplus matter which they can no 
longer hold in solution. 

The mineral matter so carried is sometimes unfavorable to both 
vegetable and animal life, bnf the most common impurities detrimental 
to man are the organic impurities which .are carried by the surfaa 
waters and sometimes also by underground waters and which have been 
taken up from areas polluted by animal life. 

With the exception of some of the mineral spring waters, mo. I ol 
the natural waters were originally potable and offered to the early 



Precipitation 33 

settler sources of supply at once obvious* and ample. Settlement has 
wrought a rapid change in these waters. Where the population is still 
small and scattered waters are still pure and satisfactory for domestic 
use, but along the streams where the larger cities are situated and 
in all thickly inhabited localities the increase of population has brought 
its unfailing results in a greater or less degree. The wastes of manu- 
facture, the sewage of cities and other refuse products of civilized 
life have found their way into the streams, seriously contaminating 
them. The ground waters are tainted with the leachings of surface 
filth and of underground vaults and cesspools, and in many cases 
while apparently not offensive are nevertheless menacing to public life 
and health by the ready means they offer for the transmission of cer- 
tain forms of diseases. As population increases, the danger of the 
presence of these organic poisons in surface waters also increases and 
with a dense population becomes almost a certainty. The same may 
be said of ground waters but in this case the contamination, being hidden 
from sight, is still more dangerous. A public nuisance which pollutes 
a stream is usually quite obvious on inspection ; a leaching cesspool how- 
ever may present a respectable surface appearance while filling the 
ground waters with filth and corruption, and the neighboring wells with 
the specific poisons or germs of the most fatal diseases. 

22. Precipitation. — All waters which occur above the ocean level 
clearly result from and are renewed by precipitation, and must of 
necessity vary in amount as the precipitation varies. While there are 
other important modifying factors that influence and control the oc- 
currence of these waters, precipitation is of greatest importance, for 
without it these waters would not exist. This is evident in many parts 
of the earth where little or no water is found on account of the almost 
total absence of precipitation. 

Various parts of the earth experience all gradations of precipitation 
from the condition of no rainfall to the other extreme found within 
the equatorial belt where torrential rains are of daily occurrence. 
Even within the limits of a comparatively small territory, the rainfall 
conditions vary widely both in quantity and distribution, and when 
these, together with the similar variations in other physical conditions 
are considered, the consequent variation in both surface and phreatic 
waters is apparent. Not only is there a great variation in average 
quantity, intensity and seasonal distribution, but in every locality there 
is likewise a great variation in the annual and seasonal amounts. 
Even the desert places are sometimes subject to intense local rains, 
Hydrology — 3 



34 Water — Its Occurrence, Utilization and Control. 

which may occasionally during a course of years visit locations ordi- 
narily devoid of rain. 

In every locality the annual rainfall is subject to considerable varia- 
tion, but the seasonal fluctuations are still more extreme, and the 
smaller the division of time considered the more radical such differ- 
ences become. In hydrological study these extreme variations be- 
come of great importance for they modify the conception of every hy- 
draulic problem involving either the utilization of, or the protection 
against the waters of streams and strata. 

23. Surface Waters. — It is evident that the surface waters are 
more widely distributed, greater in quantity, of higher utility, a 
larger source of danger and disaster, and therefore of more import- 
ance than the underground waters which are often only of local oc- 
currence. The surface and subsurface waters have, however, certain 
inter-relations and certain independent relations. In their inter-re- 
lation they must be discussed in common, but in their independent 
relations they require independent treatment. The surface waters 
therefore being of widest importance and utility need more extensive 
consideration and treatment. 

In considering the subject of circulation it has been noted that in 
general surface waters are derived from precipitation as rain or snow. 
A portion of the precipitation under ordinary topographical conditions 
flows over the lands and finally reaches more or less well defined stream 
channels through which it flows by gravity until in general it finally 
reaches the ocean. This portion of the precipitation is technically known 
as runoff or stream flow. Another portion of the precipitation is taken 
up by vegetation and utilized in plant growth ; still other portions are 
evaporated and, together with the larger portions of that taken up by 
the plants, finally add to the atmospheric moisture. Under favorable 
circumstances, still another portion sinks into the ground and is the 
source of underground waters which either remain in the strata or ul- 
timately add to stream flow or flow into the lakes and the oceans. It 
is self-evident that there must be an inter-relation among the various 
quantities of water that are used in the various ways mentioned. That 
water which is evaporated, utilized by plants or which seeps into the 
ground must limit the amounts that occur as runoff, and conversely 
every factor that affects one of these methods of disposal must also af- 
fect all others. Under favorable conditions, plant life and evapora- 
tion are most active and commonly receive and utilize the earlier por- 
tions of rainfall, especially when such rainfall is small in amount. 



Surface Waters. 35 

Pervious soil and rocks next secure their proportion and only after 
their demands are satisfied so far as conditions will permit, do the re- 
maining portions flow away over the surface. Even then evaporation 
and seepage may still be active throughout the entire flow to the sea. 
The seas are in general great reservoirs into which the streams finally 
deliver those portions of the rainfall that are not lost in evaporation 
or seepage, and in general they are the ultimate destination of most of 
the seepage waters. 

For water to exist permanently in areas below sea level there must be : 

i. An outlet or inlet to the areas from the ocean which is below ocean 
level and through which the area may be fed by the ocean ; or there 
must be 

2. An adequate drainage area which will furnish the depressed area 
with enough water to offset evaporation and supply plant life (if such 
exists). The water surface will be maintained at an elevation either 
at the elevation of the outlet from which the water will overflow or at 
varying elevations at which evaporation from the water surface will 
balance the inflow. 

For water to exist in areas above sea level as seas, lakes, ponds, 
swamps or marshes, there must be a depression below the outlet of 
the basin or the areas must have very little gradient. The water area 
must be fed by a drainage area which will furnish sufficient water to 
supply evaporation, plant life and seepage, and maintain the water level 
at varying elevations which may or may not produce overflow. 

For water to exist in streams, there must be a sufficient precipitation 
to provide for plant life, evaporation, seepage and the runoff of the 
stream. 

24. Ground Waters. — All geological deposits are more or less per- 
vious and water under the action of gravity forces its way wherever 
rock structure will admit of its presence. When the structure is fine or 
the pores between the particles small, water passes slowly ; through open 
cracks and fissures and through very porous material it moves with 
considerable velocity, and through its quality of solution it sometimes 
dissolves the rock structure and creates for itself channels of consider- 
able size. In the main, however, its occurrence is in the form of sheets 
of greater or less magnitude in the gravels, sands and sandstones, which 
sometimes underlie areas of large extent. 

These phreatic waters are replenished directly or indirectly from the 
precipitation at the points where they approach the surface. These 
waters constitute the largest factor in maintaining the low water flow 



36 Water — Its Occurrence, Utilization and Control. 

of streams and are frequently conducted to considerable distances 
and delivered into water courses from springs where cracks or fissures 
afford an outlet. Frequently they are discharged into lakes, and often 
directly into the ocean. 

Under some conditions, the water received into these deposits at 
a comparatively high elevation, is conducted between impervious lay- 
ers under lower lands where its pressure is sufficient to bring it to the 
surface in springs, if cracks occur in the overlying deposits, or as ar- 
tesian wells if the superincumbent strata be pierced by the drill. 

Where the path of the subterranean water is intersected by wells or 
by shafts, the water of the strata flows into such excavations and rises 
to the local. hydraulic gradient of the strata. Under such conditions 
it will afford a more or less abundant water supply, according to the 
nature and extent of the water bearing deposit, and of a quality de- 
pendent on the nature of the strata through which it flows. In the 
same manner these waters enter into excavations, shafts and mines 
constructed into or below the water bearing deposits, and cause a con- 
siderable expense either in the cost of excluding such waters from 
entry or in the cost of their removal by pumping. They frequently 
saturate an entire stratum and create a severe flood condition which may 
cause motion in the strata itself where the normal structure has been 
modified by excavation. This condition gives rise to land slides such 
as occur in the railroad cuts and such as have caused much trouble 
and expense in the deep cuts of the Panama Canal. 

Phreatic waters are sometimes available for public and private water 
supplies, irrigation, and in rare cases for power. 

In certain cases the condition of an unsaturated pervious subsurface 
deposit overlaid by an impervious soil with resulting swamps or 
marshes, may be obviated by draining the overlying waters through 
outlets into the pervious deposits, thus reversing the ordinary condi- 
tions. As drainage waters usually carry considerable silt, the results 
of such drainage methods are usually short-lived except for limited 
capacities or under unusual conditions. 

25. Water Supplies. — Not only is water necessary for the existence 
of animal and vegetable life, but such water must have a certain char- 
acter or it will not serve its purpose. Potable water or water which 
is not prejudicial to health when used as a source of domestic supply, 
must be free from the germs of disease, and it must also be free from 
injurious kinds and quantities of vegetable matter and of inorganic salts. 

The effect of certain forms of organic poisons upon public health has 



Water Supplies. 37 

been established by such a great expenditure of pain and of human 
life that the considerations of health must over-rule every other 
question in the selection of a source of water supply. 

When considering proposed sources of supply, these questions of the 
requisite purity of a water should receive the most careful attention. 
It is easy to define a water which is unquestionably good, and equally 
easy to define a water which is unquestionably bad. The difficulty of 
examination and determination lies not in these extremes but in the 
limiting cases. For perfect safety it might seem a simple precaution 
to reject any suspicious water, but this cannot always be done. When 
a water is simply doubtful and when a change involves a large expen- 
diture or when the rejection of a supply compels the adoption of plans 
for clarification or the adoption of a supply much more expensive to 
develop, then selection or rejection becomes a serious matter and can be 
decided only on the best of evidence. 

Water supplies for commercial and manufacturing uses must also 
have certain characteristics. For boiler purposes, waters having a 
high mineral content produce scale which is a detriment to the boiler 
and a source of expense in maintenance and as a consequence, causes 
a loss in efficiency. 

For domestic, manufacturing and industrial uses, water supplies that 
are turbid, polluted or contain a large amount of mineral matter must 
frequently be adequately treated so that the objectional qualities may 
be eliminated in order to render them suitable for the use to which they 
are to be applied. 

Suitable water supplies for agricultural uses are not so restricted in 
character. Certain organic matter, though injurious to animal life, 
affords plant food and is therefore advantageous instead of detrimen- 
tal. In the same way, certain normal constituents in solution may af- 
ford plant food, but waters highly mineralized, especially those con- 
taining large amounts of alkaline matter are harmful and sometimes 
fatal to plant life. ■ » 

For navigation and power purposes, the qualities of waters are un- 
important, so long as they are not so grossly polluted as to affect the 
health of navigators and operators or to corrode machinery. 

In every case where water is to be utilized as a supply for any pur- 
pose, the quantity must be adequate and the supply must be available 
at the time when it is needed for the purpose in view. If the average 
supply for the year is equal to the average demand and, as usually ob- 
tains, the supply varies greatly from time to time while the demand is 



38 Water — Its Occurrence, Utilization and Control. 

more or less constant, the superabundance of water at one season can 
supply the deficiency at another period only by the utilization of ade- 
quate storage. This involves the questions of evaporation, seepage and, 
in domestic supplies, the maintenance of an adequate degree of purity. 

26. Control of Water. — One of the normal functions of water is its 
cleansing property, and experience has demonstrated that the utiliza- 
tion of this function is usually the most advantageous method of tem- 
porarily disposing of those domestic and manufacturing wastes that 
can be so transported. Domestic sewage, street washings, spent dye 
stuffs and other wastes of civilized communities are therefore com- 
monly discharged through sewers to some point of disposal at a dis- 
tance from their origin and where their presence is less objectionable. 
If discharged directly into a stream they may materially increase its 
pollution, render it unfit as a source of public or private water supply 
and possibly so pollute it as to destroy the fish and convert it into an 
open sewer highly objectionable to those who live along its banks. 
With the increase of population it therefore becomes essential to pro- 
vide methods for the disposal of the wastes of a community that will 
not be detrimental to others who may occupy lower portions of the 
drainage area. 

In the practice of agriculture, which is essential to the maintenance 
of a large population, similar conditions arise. The natural sod, the 
forest covering, and even the undisturbed consolidated earth, normally 
afford a considerable degree of protection from erosion. When the 
forest is removed, the sod broken, and the soil cultivated, the condi- 
tions become more favorable to erosion ; and under certain conditions 
soil waste rapidly takes place. This occurs most rapidly on steeply in- 
clined hillsides where the runoff acquires a high velocity and conse- 
quently a great power of transportation. Where such wastes occur, there 
is not only a considerable loss of available agricultural land which can 
never be replaced, but the transported materials render the stream tur- 
bid, fill ppols and impounding reservoirs, and form bars in stream chan- 
nels to the serious detriment of water storage and navigation. These 
conditions are also important and demand consideration and control 
(see Fig. 9). 

The existence of swamps and marshes in the vicinity of centers of 
population create conditions which require attention. Swamp lands 
are not only useless for cultivation, but they are unsanitary both be- 
cause they supply the air over and around them with undue moisture 
and because they furnish a breeding ground for insects detrimental 



Control of Water. 



39 



to human life and happiness. These lands when properly drained 
often furnish some of the best agricultural lands, hence their reclama- 
tion commonly increases both the public health and the wealth of the 
community. 




Fig. 9. — Rapid Erosion in Deeply Decomposed Soil Mantle near Marion, N. C.2 

The bottom lands or flood plains along the rivers and streams of 
the country are often the direct creation of the streams which occupy 
the channel to which they are adjacent. Many of these lands are in- 
undated by every considerable flood, while others higher above the 
stream are covered only by those occasional high floods that may occur 
at rare intervals of possibly twenty or fifty years or possibly only once 
in a century or more. Attempts are often made to utilize for agricul- 



2 Denundation and Erosion in the Southern Appalachian Region, by L. C. 
Glenn. Prof. Paper 72, U. S. G. S. 



40 Water — Its Occurrence, Utilization and Control. 




Fig. 10. — Map of Dayton, Ohio. Shaded Portion Shows Area Flooded in 
March, 1913. Ground Saturated; Rainfall in Four Days about Nine 
Inches (see page 41). 




Fig. 11. — Dayton, Ohio. Flood of March, 1913 s (see page 41). 



s From Report of A. E. Morgan, Chief Engineer Miami Conservancy Dis- 
•ict 



Control of Water. 41 

tural purposes lands which are frequently inundated. When these 
floods occur after crops are planted or before they are harvested as is 
often the case, considerable losses are entailed and works for the pro- 
tection of such lands are in frequent demand. 

The level land adjacent to streams furnishes desirable building sites, 
and the absence of floods, save at rare intervals, has in some cases in- 
duced the development of communities and industries in locations which" 
are occasionally exposed to serious overflow. To secure valuable lands 
and to cheapen the construction of bridges, even the natural channel of 
the stream is often restricted, and occasionally such channels are so lim- 
ited that when the rare extreme flood does occur, these channel 
restrictions and structures built in the natural path of the flood, cause 
congestions which result in great losses of life and property, (see Figs. 
10 and n, page 40). 

The protection of communities from such losses, often occasioned by 
their own folly and short-sighted policy, becomes a matter of the utmost 
importance. 

In a similar manner, and for commercial purposes, many large com- 
munities are located on the low lands adjacent to the large bodies of 
water such as the lakes and oceans. Frequently also the lands border- 
ing these waters are valuable for agricultural purposes. Lands so lo- 
cated, which are perhaps inundated only at high tide, can sometimes be 
reclaimed by the construction of suitable protective works which must 
not only hold back the water but be sufficiently substantial to withstand 
the effects of currents and waves to which they are exposed. Such 
lands are also occasionally subjected to extreme, conditions resulting 
from extraordinarily high tides and heavy waves which may occur only 
at rare intervals under unusual storm conditions. 

27. Necessity for the Study of Hydrology. — It is apparent that in 
order to meet intelligently the manifold conditions that arise in connec- 
tion with the utilization of water for the many purposes to which it 
must be applied, and its control in the interests of human health, hap- 
piness and prosperity, the entire subject of its distribution and cir- 
culation on and within the earth's surface must be investigated and 
understood. To utilize or control these waters to the best advantage, 
the engineer must know the principles that underlie their circulation, 
the regularity or irregularity of their occurrence, their quantities, quali- 
ties and distribution, and the possibilities of retaining, storing, regulat- 
ing and controlling their flow and their use. The subject is not a simple 
one for the elements of these problems include the great cosmical laws 



42 Water — Its Occurrence, Utilization and Control. 

which are understood only imperfectly but on which depend the changes 
and variations of the season. They include the principles of meteoro- 
logy, the science that treats of atmospheric conditions and changes, also 
the principles of geology which treats of the past and present conditions 
of the earth's surface and the causes and results of topographical growth 
and development. All of these subjects must be considered in their 
hydrological relations and in connection with the subjects of hydraulics 
and hydrodynamics, which treat respectively of the laws of flow of 
water and of its power in motion. To secure the best perspective of 
this complicated subject, pertinent conditions that obtain must be ob- 
served and interpreted in the light of scientific knowledge as at present 
developed, in order that the various phenomena may be understood and 
correctly correlated and applied to the solution of the present problems 
with which the engineer has to deal. 

LITERATURE 

RELATING TO GENERAL HYDROLOGY AND' HYDROGRAPHY 

Water Supply and Irrigation Papers, United States Geological Survey. 
Report on Water Supply of New Jersey, C. C. Vermeule, Vol. 3, Geological 

Survey of New Jersey, 1894. 
Water, Its Origin and Use, William Coles Finch. 1909. D. Van Nostrand and 

Company. 
Annual Reports, United States Geological Survey. 
Professional Papers, United States Geological Survey. 
Bulletins, United States Geological Survey. 
Annual Reports, United States Reclamation Service. 
Annual Reports, United States Weather Bureau. 
Bulletins, United States Weather Bureau. 
Monthly Weather Review, U. S. Weather Bureau 
Daily Riv.r Stages, U. S. Weather Rin-^au. 

Annual Reports of the Chief of Engineers, United States Army. 
Reports on Drainage Investigations, U. S. Department of Agriculture. 
Reports on Irrigation Investigations, U. S. Department of Agriculture. 

Detailed reference to the principal publications relating to various special 
subjects will be found under the special chapter to which the subject matter of 
the respective publications more especially refer. 



CHAPTER III 

SOME FUNDAMENTAL THEORIES 

28. Growth and Development. — Even limited observation of ma- 
terial objects will show that all things are subject to continual changes 
in both form and condition ; that nothing on earth is permanent but 
that all things are passing through a continuous evolution. 

Organic life develops from the seed and passes through youth to ma- 
turity, old age and death. A similar transition takes place in the case 
of inorganic forms and the conditions resulting therefrom. A contin- 
ual change is apparent, visible in the more stable forms perhaps only 
through long observations but no less actual when centuries are con- 
sidered. A careful study furnishes convincing proof that everything is 
subject to growth and development and to final decay and dissipation. 
Nature is never stationary but always progressive, and the character of 
its progress, its trend and destination within the limitations of the 
life of a man or a nation may be of great importance in considering 
engineering works of magnitude and of comparative permanency. 

Of the origin and conditions of things and of the nature of the ulti- 
mate evolution from present conditions, science furnishes no informa- 
tion and speculation can arrive at nothing definite. Science must deal 
largely with the conditions of the present. It may go back a few ages 
in the life of the earth by reading from the geological record the condi- 
tions that have prevailed in ages comparatively recent, and in the same 
manner it may forecast the future for a few years, insignificant perhaps 
in comparison with the limits of eternity but sufficient at least for the 
practical purposes of mankind. 

29. Past Conditions and Their Evolution. — At one period in its his- 
tory the earth was probably at. such a temperature that no water ex- 
isted even in the form of vapor, the temperature being so high that 
the association of oxygen and hydrogen as aqueous vapor was impos- 
sible. With the gradual reduction of temperature, chemical union 
first became possible, and as the reduction proceeded vapor was 
formed, condensation took place and the first precipitation occurred. 
With the high surface temperature of the primitive earth crust, evap- 
oration rapidly followed and circulation was both rapid and violent, 
the resulting effects on the modification of surface forms beinsr corre- 



44 Fundamental Theories. 

spondingly great. As soon as the temperature reductions were suffi- 
cient to permit of the existence of water in stable liquid form, the de- 
pressions of the crust began to fill and the changes from primitive to 
present forms began. 

The present condition of the earth's surface is the result of pre- 
vious conditions and numerous forces which have been in action since 
the beginning of time and are still in action. 

The intensity of the action and the resulting effects have undoubt- 
edly, varied with the prevailing conditions and while the engineer can 
have but a poor conception of the great changes that have occurred in 
the past and the forces which have produced them, he can by study and 
investigation obtain a sufficiently clear idea to enable him to understand 
the causes of many of the present conditions and the forces which are 
now acting and which must be utilized or appreciated to bring about a 
successful outcome of his work. 

30. Fundamental Considerations. — It is necessary for a proper ap- 
preciation of the subject to consider certain fundamental conditions 
which underlie all problems concerning the earth and the continual 
changes which are in progress. 

Powell has pointed out x that the earth is encompassed by three en- 
velopes each active and changeable to a greater or less extent. 

First.— The rock envelope or lithosphere. 

Second. — The aqueous envelope or hydrosphere. 

Third. — The air envelope or atmosphere. 

These envelopes are inter-active one on the other and a complete 
knowledge of one necessitates a practically complete knowledge of the 
others on account of the mutual relations. 

T,ittle is known concerning the great central mass of the earth, for 
the deepest mine or the deepest borehole has penetrated the outer 
crust or rock envelope for only a few thousand feet. 

The rock envelope consists of masses of rock of various degrees of 
hardness, porosity and homogeneity arranged in both stratified and un- 
stratified layers and beds, and in heterogeneous piles. The rock masses 
are physiograpbicallv arranged in mountains, hills, valleys, plateaus, 
plains, and in swamp, lake and ocean beds, all quite clearly defined in 
outline but projecting into both the air and water envelopes and ad- 
mitting these envelopes into their structure through caverns, crevasses, 
cracks and pores. 

1 Physiographic Processes by J. W. Powell. 



Fundamental Considerations. 45 

The water envelope covers more than three-quarters of the earth's 
surface and hydrographically consists of oceans, seas, lakes, swamps, 
streams, snow and ice fields, ground waters, aqueous vapors and clouds. 

The atmosphere covers the earth and waters to a great depth, and 
develops in its mass winds, cyclones and tornadoes. 

The envelopes are always in motion and always changing but not with 
the same degree of rapidity. The rock envelope is apparently the 
most stable ; that is, its changes occupy a greater length of time than 
aqueous and atmospheric changes, but the changes are no less radical 
and complete. The sea bottom of one age becomes the plains, pla- 
teaus .or mountain tops of another age ; the hills become valleys, and 
the mountains islands, for the land though apparently stable is only 
relatively so and is rising or falling, receiving accretion or being eroded 
and carried to other localities. 

The water envelope is less stable and more actively changing : the 
snow and ice fields melt and with the rainfall form rivers, and the 
rivers run to the sea ; the waters of the land and sea evaporate or va- 
porize into atmospheric moisture, condense into rain, snow and other 
forms and in such changes radically affect both the rock and atmos- 
pheric envelope. 

The atmospheric envelope is still less stable and its changes from 
calm to storm, are more radical and apparently more erratic. 

These envelopes are interacting among themselves. Each is affect- 
ing the others ; each is modifying the activity of the others and may be 
either reducing or accelerating such activity. 

31. The Atmosphere. — The earth's atmosphere has most import- 
ant influences on the evaporation of water, the distribution of aque- 
ous vapor, and its precipitation. While evaporation would take 
place regardless of the atmosphere, yet the atmosphere being always 
present modifies and controls the prevailing conditions. The atmos- 
phere extends outward from the surface of the earth with diminish- 
ing density for an unknown distance. The sensible height to which it 
extends is about fifty miles, for although at this distance the density 
is not sufficient to produce a measurable pressure, yet its presence in 
an appreciable amount is made manifest by the diffraction of the rays 
of the setting sun. That the atmosphere extends to a much greater 
distance than this has been shown by observation of meteors which 
become luminous on entering the atmosphere. 

"At heights greater than about nine miles the temperature remains 
nearly constant at about — 70 Fahr. and is known as the isothermal 



46 Fundamental Theories. 

or advective region. The atmosphere of this region appears prac- 
tically free from water vapor and takes no active part in circulation." 2 

The air is composed of four principal gases which are in mechanical 
mixture only. These gases in the proportion by volume present in a 
normal sample of air are : 

Nitrogen 78.04 per cent. 

Oxygen 20.99 P er cent - 

Argon 00.94 per cent. 

Carbon Dioxide 00.03 P er cent. 

This analysis is not exact for all cases since the percentage of the 
various gases varies with the geographical location, elevation and local 
conditions. 

As the elevation increases the nitrogen and oxygen of the atmos- 
phere diminish in quantity and at the highest elevation probably little 
trace exists of any gas but hydrogen. 

The atmosphere besides furnishing the gases necessary for the sup- 
port of plant and animal life, contributes its offices in other ways to the 
activities of the earth's inhabitants. It carries bacteria, plant spores 
and the winged seeds of various large plants ; the flight of insects, 
birds and man is made possible by its presence ; sound would be im- 
possible were it not for the presence of the air. By virtue of its cir- 
culation over the surface of the earth, it supplies power to drive sail- 
ing vessels and furnishes power to wind mills ; it transports moisture 
from the sea and precipitates it over the land ; it assists in the weath- 
ering of rocks and by its movement produces waves in the sea. 

While the composition of the atmosphere is approximately constant 
at all points on the earth's surface yet on account of the relations of 
different points of the earth's surface to the sun and on account of the 
differences in relations of sea and land surfaces, the physical condi- 
tions of the atmosphere differ from place to place and from time to 
time in the very important matter of temperature. The range in the 
extremes of temperature vary from perhaps — 90 to i,8o° Fahr. and is 
small compared with the extreme range of temperatures known to 
science yet it gives rise to the variations from the ever frozen polar re- 
gions to the heat of the desert. 

32. Atmospheric Temperatures. — Atmospheric temperatures, 
which are important factors in atmospheric circulation and hence in 
the distribution and occurrence of moisture and precipitation : 

First. — Decrease from the equator to the poles. 
2 Climate and Weather. H. N. Dickson, p. 76. 



Atmospheric Temperatures. 



47 



Second. — Decrease with altitude above sea level. 

Third. — Increase with the advent of day and decrease at night. 

Fourth. — Decrease as the surface of the earth receives the more in- 
clined rays of the sun, due to the revolution of the earth in its solar 
orbit, and 

Fifth. — Vary with the winds, and with the relative humidity. 



Temp 


an 


pti 


Temp 


an 


pn 


/ 23 4 5 


6 7 5 9/0 


in 


?/ 


z\: 


4. 


">\6\7\B\9 


101 


/;■ 


i , 


'3 


4. 


l r, 


7 


8 


9 10 II 12 1 


2 


3 


4 . 


' t 


r 8 9 10 II 12 


70° 

60° 
50° 

3<f 














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70° 
60° 
30° 
40° 


































s.oJr 








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,' 










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. 































Fig. 12. — Mean Diurnal Changes in Temperature at Various Stations in the 
United States (see page 48). 

The heat changes at the earth's surface are of great importance. 
Practically all of the heat received at the surface is from the sun. 
Various rays from the sun received through the earth's atmosphere 
give rise to various colored light, produce certain chemical effects, and 
when stopped by opaque objects are converted into heat. 



~-'-r 


/an 


Feb Mar 


-:w- 


■,% 


/i -e 




Qua. 


:rcr 




V:. 


Dec 


Temp 




■'..- 




Mc 


Mai/ \june 


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' 


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100° 
80° 
60° 
40° 
20° 
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100° 
80° 
60* 
40° 
20° 
10° 
























































































































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Fig. 13. — Mean Annual Variations in Temperature at Various Stations in the 
United States (see page 48). 

Atmospheric temperatures are the result of the heat received from 
solar radiation, both directly by absorption of heat from the solar 
rays, and also indirectly by contact with and radiation from the surface 
of the earth. While it is generally believed that the earth's interior still 
remains at a high temperature, the earth's crust is such a poor con- 
ductor of heat that this interior heat has very little effect on surface tem- 
peratures or surface radiation, and the temperature of the earth's sur- 



48 



Fundamental Theories. 



face and of the atmosphere is therefore controlled largely by solar 
radiation. 

Even in midsummer with the sun at the meridian, its rays reach 
the earth's surface in polar regions at a considerable inclination, 
while between the tropics the inclination is comparatively small. The 
distance of the earth from the sun and the altitude of the sun at the 
meridian therefore vary least during the year at the equator and 
most at the poles. In consequence the greatest difference in tem- 

70 




Dec Jan. Feb. Mar. Apr. May June Ju/y Aug. Sept. Oct. Nov. Dec. 
Fig. 14. — Variations in Temperature of Air, Water and Earth at Hamburg, 
Germany (see page 49). 

perature between day and night occurs at the equator and the least at 
the poles ; while the greatest annual variation between winter and 
summer occurs at the poles and the least at the equator. 

The conditions above described give rise to diurnal (see Fig. 12, 
page 47) and annual (see Fig. 13, page 47) changes in atmospheric 
and surface temperatures. 

Of the incident solar heat, the atmosphere absorbs an average of 
about 76 per cent, about 50 per cent being absorbed by a cloudless and 
practically all by clouded atmosphere. 3 Of the solar heat reaching 
the earth's surface, four times as much is absorbed by the land as by 
the water surface. 

The solar rays falling on soils and rocks are absorbed and converted 
into heat, the effect or warmth depending on the specific heat of the 
substance and its conductivity which vary greatly with different depos- 
its. Loose, porous, air filled soils conduct heat slowly, while solid clay 
soils especially when saturated with water convey heat very rapidly. 



3 See Descriptive Meteorology, W. L. Moore, p. 78. 



Atmospheric Temperatures. 49 

The latter are therefore readily heated and quickly cooled and are sub- 
ject to a great range of temperature. The former warm but slowly and 
retain their heat which during radiation is replenished from the lower 
strata ; hence such soils or substances have a small range of tem- 
perature. The immediate surface areas of the earth undergo the great- 
est seasonal variations in temperature. As the depth below the surface 
increases, these variations decrease until a constant temperature prevails 
which is the balance between the average external and the internal tem- 
peratures (see Fig. 14, page 48). 

Water is diathermanous, and the absorption of solar heat takes place 
only gradually from the surface to considerable depths. Its specific 
heat is very high, hence it has the capacity to absorb and give off great 
quantities of heat. This results in reducing the range of temperature 
variation over a sea as compared with the land. Sea water also de- 
creases in specific gravity with a rise in temperature which tends to 
cause the warmer waters always to lie at the surface. In the .case of 
fresh water, however, the temperature of greatest density is 39. i° Fahr. 

The snow and ice covering of the higher latitudes obliterates the dif- 
ference between land and sea. Snow contains a large amount of air 
and is in consequence a poor conductor of heat ; hence the range of 
temperature is considerable but is limited in its rise to the melting point. 
In the temperate zone the snows of winter delay the warming of the soil 
in spring inasmuch as heat is absorbed by the melting of snow and in 
its evaporation. The greatest seasonal differences of temperature be- 
tween sea and land occur in intermediate latitudes where the summer 
heat is intense. 

The annual variations in temperatures of the air, of the waters of 
the River Elbe, and of the earth to a depth of 16.4 feet at Hamburg, 
Germany, are shown in Fig. 14, page 48.* 

The surface temperature of the ocean is considerably disturbed and 
modified by ocean currents but in a general way these temperatures 
may be stated as follows : 

SURFACE TEMPERATURES OF OCEAN (MOORE) 

Geographical Location Annual Change 

At Equator 82° 84° Fahr. 2° 

At Latitude 35° N. or S ■. 50° 68° Fahr. 18° 

At Latitude 70° N. or S 35° 45° Fahr. 10° 

The net result of the various factors above described is to produce a 

4 Ibid, page 91. 

Hydrology — 4 



50 



Fundamental Theories. 



6C SO' 




Fig. 15. — January Isotherms (see page 51), 



90' GO' W 




Fig. 16. — January Isobars (see page 51). 



Atmospheric Pressures. 



51 



somewhat irregular distribution of temperatures on the earth's surface. 
This distribution throughout the world for the months of January and 
July is shown by the isothermal lines on Fig. 15, page 50 and on Fig. 18, 
page 52, respectively. These lines represent the mean isotherms for the 
respective months and are modified from year to year by meteorological 
conditions. They are also modified locally by the passage of storm 
centers and by anti-cyclonic movements. 

33. Atmospheric Pressures. — The heat acquired by land and 
water surfaces is in turn radiated into or through the atmosphere, thus 
in turn affecting atmospheric temperatures. Atmospheric temperatures 
and their variations are the direct cause of atmospheric pressures and 






'///////////////////////A?//////////////////////////////////////^^^ 

Heated Area- 

Fig. 17. — Circulation Due to Heated Area. 

their variations. The expansion of the atmosphere 6y heat causes an 
overflow from above the heated area, a local or planetary circulation in 
accordance with the extent of the heated area (see Fig. ly), and a con- 
sequent decrease in surface pressure on the heated area. In conse- 
quence of this law and the relative gain and loss of heat by the ocean 
and land areas at various seasons, the land areas attain their maximum 
pressure in winter and their minimum pressure in summer, while these 
conditions are reversed on ocean areas. (See Fig. 16, page 50 and Fig. 
19, page 52, in which the lines represent mean atmospheric pressure for 
the respective months in terms of inches of mercury. These maps should 
be compared with the maps showing the isothermal lines for the same 
period which are shown just above them in Figs. 15 and 18 respectively). 
For the same reason there is a daily fluctuation in the local barometric 
pressure, the minimum occurring shortly after the maximum heat of the 
day. (See Fig. 20, page 53 and Fig. 21, page 54.) These fluctuations 



52 



Fundamental Theories. 



120' iSO f 




Fig. 18. — July Isotherms. 



izo' i5d!_ iaoi iso ijtf so' 




Fig. 19. — July Isobars (see page 51). 

are often obscured by non-periodic changes caused by the passage of cy- 
clonic centers or anti-cyclonic centers of disturbance. 

Normal atmospheric pressure should be symmetrical and practically 
the same in all places having a common altitude, for the pressure should 



Atmospheric Pressures. 



53 



Ch/caao,I//. /SPA 


Month 


1 


I 


t\l 


t*> 


* 


*> 


Vfc 


K 


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i 


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k 


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^J 


Jan 

Feb 
Mar 

Apr. 
May 

June 
July 

dug. 

Sept 
Oct. 

//or. 
Pec. 


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./O 
.09 

29/6 
/5 
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.13 

14 

.13 

29.Z2 

25 

.24 

23 

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09 
.06 
.07 
V6 

/7 
29. /6 

./5 

J3 

29/2 
// 

2b 

29.24 

23 
















































































































































. 
























































































































































































































































































































































































































































































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2922 
.21 
20 

29/7 
/6 
.15 

J5 
29^4 
J3 
J2 
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Fig. 20. — Monthly Mean Diurnal Pressure Changes at Chicago. 

be equal to the weight of the column of air above the point under con- 
sideration, which should be the same for all places of the same height 
above sea level. The normal atmospheric pressure at sea level is equiv- 
alent to the pressure of about 30 inches of mercury or 14.7 pounds per 



54 



Fundamental Theories. 



square inch which value may vary however about one and one-half per 
cent., with the ordinary changes in atmospheric pressure. Normal at- 
mospheric pressure decreases with the height above sea level, and this 
decrease may be calculated by the formula 

H 
(1) Log b = 1,47712 



in which 



64000 



b = average barometer reading in incbes of mercury. 
H = height of station above sea level in feet. 



R-es 


AM 


F*M. 


/ 


2 


3 


4 


5 


e 


7 


a 


S 


IO 


II 


IZ 


I 


Z 


3 


4 


5 


6 


7 


e 


9 


/o 


II 


IZ 


30.J 


















































30.0 




















r/e_ 


7Q3 




























299 


















































?9ft 


















































PA 7 


















































P.96 


















































P95 




















- 






























294- 
















s& 


Lo 


yis 






























P93 


















































?.$? 


















































29/ 
















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lA 


w 






























pan 





































































































Fig. 21. — Diurnal Pressure Changes at Various Stations (see page 51). 

The average pressure per square inch at various elevations above sea 
level can be determined directly by the following modification of for- 
mula ( i ) : 



H 



(2) Log P = 1.16801 



64000 



in which 



F — the atmospheric pressure per square inch in pounds. 
H = elevation of station above sea level in feet. 

In Table I are given the avenge annual barometiic readings at vari- 
ous points in the United States as determined by the United States 
Weather Bureau for 1890 and 1891, with the height of the location of 
the barometer above sea level and the pressure calculated by formula 
(i)- 



Atmospheric Pressures. 55 

TABLE I 
Comparison of Observed and Calculated Barometric Heights 

Elevation Average 
Station above sea annual Calculated 

level barometer barometer Difference 

Key West, Fla 22 30.02 29.97 —.05 

New Orleans 54 29.96 29.94 —.02 

Philadelphia 117 29.85 29.87 +.02 

Memphis, Tenn 330 29.66 29.65 —.01 

St. Louis 571 29.36 29.38 +.02 

Cincinnati 628 29.32 29.33 +.01 

Detroit, Mich 724 29.16 29.23 +.07 

Chicago - 824 29.06 29.12 +.06 

Bismarck, N. Dak 1,681 28.20 28.24 +.04 

Ft. Assinniboine 2,690 27.02 27.21 +.19 

Salt Lake 4,348 25.23 25.66 +.43 

Santa Fe, N. Mex 7,026 23.24 23.30 +.06 

On account of the disturbing influence of the sun's heat, and the 
consequent movement of air currents a considerable variation is 
caused in barometric pressures, these pressures varying with the diur- 
nal rotations and annual revolutions of the earth. The diurnal varia- 
tion in atmospheric pressures is illustrated by Figures 20, and 21, 
pages 53 and 54. Fig. 16, page 50 and Fig. 19, page 52 show the 
sea level isobars for January and July. "From what has been said it 
will be seen that there is a close relation between temperature and 
pressure. High temperature expands the volume of the air and causes 
an overflow at high levels and a decrease in the pressure at the sur- 
face. The result is that land areas have maximum pressures in winter 
and minimum pressures in summer, while the reverse is true of ocean 
areas. Regions of considerable elevation also have a maximum of 
pressure in summer for the reason that when the air is cold and dense, 
a greater percentage of the mass is below this level than is the case 
when the air is expanded by heat." 5 

34. The Planetary Circulation. — Atmospheric circulation is pro- 
duced by the following causes : 

First. — The atmosphere rotates with the earth, of which it forms a 
part. 

Second. — The atmosphere, heated at the tropics, rises and flows to- 
ward the poles, as it is cooled, it settles and produces lower counter 
currents towards the tropics. 

Third. — The mixture of aqueous vapor with the atmosphere and the 
liberation of heat during precipitation, produce and accentuate vertical 

5 Ibid, p. 136. 



56 Fundamental Theories. 

currents which greatly modify the velocities, altitudes and direction of 
atmospheric currents. 

Fourth. — Irregularity in the topographic features of a country causes 
marked changes in the direction of the lower winds, and produces eddies 
and irregularities in the lower air currents. 

Fifth. — Variations in local temperatures of land or water sometimes 
modify the local atmospheric currents to a considerable extent. 

The very great number of possible relations and combinations among 
these various causes of atmospheric movements make the winds at 
lower altitudes seem erratic, while those in the higher altitudes, being 
free from local influences, are more largely governed by the two first 
.normal and principal causes. 

It is evident from what has already been presented that circulation 
is primarily caused by differences in temperature on the earth's surface, 
which in turn produce difference in pressure and, consequently, atmos- 
pheric movements. The general circulation of the atmosphere is due 
to the unequal heating of the earth's surface by the rays of the sun. 
The effect of this is to cause an expansion and consequent ascending 
of the air in equatorial regions, a poleward flow of the upper atmos- 
phere, a cooling and consequent contraction, descending current and 
in the lower regions a movement toward the equator. This movement 
is greatly modified by various causes. 

An important principle that has a marked effect upon the atmos- 
pheric circulation should here be noted. In a planet revolving on its 
axis with a certain velocity, the attraction of gravity in the direction 
of the center of the sphere, combined with the centrifugal force of ro- 
tation, will have a tangential component toward the equator at every 
point except the poles. The component is offset in the planets by the 
gradual increase in the radius from the poles to the equator which radius, 
to obviate the development of a component poleward or toward the equa- 
tor, would have to be reduced if the velocity of rotation decreased and in- 
creased if the velocity of rotation should be increased. It follows there- 
fore that any body moving on the surface of the earth under any in- 
dependent force, and in a direction having a component in the direction 
of the earth's rotation, will move in space with a velocity in its latitude 
greater than the earth's rotation, therefore the centrifugal force will 
increase and a component will develop toward the equator. 

In a similar way, any body moving with a westerly component is 
moving through space slower than the earth in its latitude ; its centrif- 
ugal force will therefore diminish and a component will be developed 



Planetary Circulation. 57 

toward the pole. This general principle is known as Fertel's Law, and 
may be stated as follows : Every body moving on the surface of the 
earth is deflected to the right in the northern hemisphere and to the 
left in the southern hemisphere because of the earth's rotation. 

At the equator, the earth's surface and the atmosphere in contact 
with it, which is relatively stationary, have an actual velocity in rotation 
of about 1,000 miles per hour; the rotative velocity of the surface de- 
creases poleward and becomes zero at the poles. The difference in 
the relative rotary speed at the equator and poles gives an easterly di- 

Norf-h Pole 

South Westerly Variables 

30°35h/j£^ / ^\.Tropical 'dry belt The^Horse Latitudes' 

N.E Trade Wind 

EquatoA Equatorial ' be/r ofca/ms and rains 

The Doldrums 

5. E Trade M'nd 
J0°JS5\^ \ \ ~^i" Tropical dry belt. The'tlorse Latitudes" 

North h/esfer/y Variables. The Poaring Forties' 

5outh Pole 
Fig. 22. — Planetary Circulation on a Uniform Planet (see page 58). 

rection to the upper poleward flowing warm air currents, and from the 
same causes the lower return currents are given a westerly direction. 

The upper currents, free from the frictional resistance of the earth, 
acquire high velocities (perhaps 300 miles per hour or more) and a 
spiral movement in their flow. As the path becomes more nearly par- 
allel to the equator, the centrifugal force due to this high velocity, in 
the direction of the rotation of the earth, tends to force the air toward 
the equator in accordance with Ferrel's Law. The return currents 
from beyond the parallels of 30 degrees are in general deflected west- 
ward and hence crowd the air poleward. Thus the effect of both 
movements is to produce a maximum atmospheric pressure between 
the parallels of 30 and 40 degrees. 

The pressure near the equator is always less both on account of the 
temperature and the centrifugal force of the earth's rotation. In the 
region of the poles, the temperature tends to cause an increase in at- 




58 Fundamental Theories. 

mospheric pressure which is somewhat offset by the deflecting forces- 
above described. Half of the earth's area is. included between the 
parallel of 30 degrees north and 30 degrees south, and in general the 
ascending currents, strong at the equator, decrease poleward toward 
the limits of this belt. The descending currents which in general must 
occupy a similar area, occur in latitudes beyond this belt. The net re- 
sult of these forces is the distribution of atmospheric pressure shown 
in Fig. 16, page 50, and Fig. 19, page 52. The low pressure belt at the 
equator and the high pressure belts between the parallels of 30 and 40 
degrees are regions of little horizontal atmospheric movement and of 
calms. 

Fig. 22, page 57 G shows the planetary circulation as it might exist om 
a planet with uniform surface and unmodified by the variation of to- 
pographical and temperature relations which actually exist on the 
earth's surface. As would naturally be assumed, the actual develop- 
ment of this theoretical planetary circulation obtains only when the 
earth's surface most nearly coincides with the theoretical assumption 
of uniformity of surface, namely on the oceans, and this circulation is- 
elsewhere modified by the variations in surface conditions. 

LITERATURE 

Atlas of Meteorology, J. G. Bartholomew, Royal Geographical Society, Edin- 
burgh, 1899. 

Climate and Weather, H. N. Dickson, Henry Holt & Co., New York. 

Modern Meteorology, Frank Waldo, Charles .Scribners Sons, New York, 1893. 

Meteorology, Willis I. Milham, The MacMillan Co., New York, 1912. 

Descriptive Meteorology, Willis L. Moore, D. Appleton & Co. New York, 1910. 

Handbook on Climatology, Dr. Julius Hann (Translated by Robert de C.- 
Ward) The MacMillan Co., New York, 1903. 

Meteorology, Thomas Russell, The MacMillan Co., New York, 1895. 

Elementary Meteorology, W. M. Davis, Ginn & Co., Boston, 1902. 

Physiographic Processes, J. W. Powell, American Book Co., 1896. 

College Physiography, R. S. Tarr and L. Marten, MacMillan Co., 1917. 

Elements of Geography, Salisbury, Burrows and Tower, Henry Holt Co., 1912.. 

Physiography, Rollin D. Salisbury, Henry Holt & Co., 1913. 



e See "Climate and Weather," by H. N. Dickson, p. 90. 



CHAPTER IV 
WINDS AND STORMS 

35. Permanent Winds. — Permanent winds are found more particu- 
larly on the ocean where the planetary circulation is not modified by 
topographical conditions (see Fig. 23, page 60). As the air descends 
in the belts of maximum pressures it, of course, enters an area of 
greater density, and because of the resulting increase in temperature, 
is dry ; hence land areas lying within these belts include nearly all of 
the permanent desert areas. 

The trade winds which originate in these high pressure belts near 
latitude 30 are among the most constant of the permanent winds. 
They occupy belts from 12 to 25 of latitude on both sides of the 
equator, occur at sea some distance west of the continental masses, 
and blow toward the equator ; light at first, they become stronger as 
they advance and are deflected more and more toward the west. Being 
fed chiefly from the descending air in the high pressure belt, the trade 
winds are dry winds in the higher latitudes and therefore in some 
cases create desert conditions close down toward the equatorial belt. 
They are permanent and persistent winds, varying in strength but 
seldom shifting in direction more than a few degrees. 

Between the trade wind belts under the meteorological equator is a 
region of light and irregular winds called the Belt of Calms. The anti- 
trade winds are the winds of the upper atmosphere, opposite in direc- 
tion to the trade winds. 

The prevailing westerlies are the winds of the high latitudes which 
blow in general from the west. These are of greatest intensity be- 
tween 40 and 50 south, and blow with greater force than the trade 
winds. While their movement is in general toward the eastward, there 
are occasional periods where locally the wind may not blow from the 
west. The winds of high northern latitudes, while of great force, are 
variable on account of the interference of cyclonic disturbances due to 
continental areas. These winds in the United States blow in general 
with a westerly component more than half of the time. 

36. Periodic Winds. — In certain regions, namely, India, East Africa, 
North Australia and the Lower Mississippi Valley there is an almost 



60 



Winds and Storms. 




Periodic Winds 




40° 




Z0° [ 



20° 



40° ~ SO" 60° 70° 80° SO" J00° 110° 

Fig. 24. — Directions of the Monsoons of the Indian Ocean (after Bartholomew) 

(see page 62). 



62 Winds and Storms. 

complete reversal of wind direction between winter and summer; 
while in Spain, Eastern North America and British Columbia, there is 
a decided change in wind direction. The most striking example of 
periodic winds is the monsoon winds of the Indian Ocean (see Figs. 
24-A and 24-B, page 61). These monsoon winds are caused by the 
movement of the colder air to the warmer regions during the seasons 
of summer and winter, and are usually denned as winds which blow 
for six months of the year from one direction and for the other six 
months from the opposite direction. They are, however, greatly in- 
fluenced by the planetary atmospheric circulations and by topographi- 
cal features, and the complete reversal of direction seldom takes place. 
The land and sea breezes, so named because of their blowing alter- 
nately from the land or from the sea, are caused by the radiation and 
consequent greater heating of the atmosphere over the land by day 
and over the sea by night. Mountain and valley breezes are similar 
in nature and are most highly developed where deep valleys open into 
broad plains. 

37. Non-Periodic or Irregular Winds. — The normal tendencies of 
direction of the air current in the planetary circulation in contact with 
the earth's surface are greatly affected by the larger topographical feat- 
ures of the land which they meet, and by the seasonal temperature 
changes, and they are often entirely obscured by encountering currents 
and circulations which are often of a more violent though less exten- 
sive character. The planetary circulation is also modified in direction 
and intensity by the difference in temperature between land and sea, 
and the temperature irregularities in each, and there is thus produced 
secondary centers of atmospheric action which, according to their loca- 
tion, character and intensity, are classed as cyclones, hurricanes, ty- 
phoons, thunder storms and tornadoes which pass across the country 
at frequent but irregular intervals. Other non-periodic winds more 
local in character are still more greatly modified by topographical and 
geographical features. Such winds are the Foehn, Chinook, Sirocco 
and Mistral. 1 

38. Cyclones and Anticyclones. — Cyclones are the great rotary at- 
mospheric movements which center around low pressure areas. They 
appear at irregular intervals and progressively pass across the country 
in a general easterly direction. The greater part of the rainfall, par- 
ticularly that which takes place within the interior of the continent, is 



1 See Meteorology, by Thomas Russell. 



Cyclones and Anticyclones. 



63 



due to winds of this class. These winds are believed to originate as 
vortices in the great planetary circulation but are modified by a more 
or less local or regional heating of the earth's surface! which causes 
•a decreased pressure over the area so heated and promotes an inflow 
from all sides to supply the ascending current, and this vertical circu- 
lation is maintained so long as the surrounding atmosphere is in a state 
of unstable equilibrium. The air in the lower portion, as it flows in 
from all sides, derives a circular or gyratory motion from the rotation 





\ 1 y^&\ 




'o 

Ja/ 


S, c .Marie 


T"\ A 3 

roCLvorK 

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7 [~^9 - \ \ 

fwsn 


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1 San /r^V. • ^/-. 


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J/ I Denver 


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vii T°A 


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— - Lj "~UT7Pa 


o 


OAbilenV^V P V (X 

M /3°° > 



Fig. 25. — Typical Areas of High and Low Pressures 3 (see page 64). 

of the earth, similar to the vortex formed in water running out through 
an orifice in the bottom of a shallow basin. 2 In the northern hemi- 
sphere, this circular motion is counter-clockwise, but has the reverse 
direction in the southern hemisphere. The area within the cyclone, 
where the barometric pressure is less than that in the surrounding 
area, is called the "area of low pressure." It is the center of the 
storm and marks the area of ascending air currents. At and near this 
center there is a calm area of greater or less extent, depending on the 
•dimensions of the cyclone. 

In the region of maximum pressure the air does not descend in a 
vast uniformly flowing mass but in extremely variable, somewhat lo- 



2 See Ferrel's Law, Sec. 33, p. 57. 

s Figs. 25 to 30 inclusive are taken from Bulletin No. 20, U. S. Weather 
IBureau on "Storms, Storm Tracks and Weather Forecasting." 



64 



Winds and Storms. 



calized descending currents, some of them of strong intensities and 
some weak. The stronger of these movements, which occur around 
the outer areas of maximum pressure, strike the earth and because of 
the friction of the earth surface and of the effect of the* earth's rota- 
tion are deflected to form eddies in the atmosphere of high pressure 
called anti-cyclones. The atmospheric movements due to the pressure 
variations are relatively light and the consequent anticyclonic circu- 
lation is slow. The result is that such systems do not endure for any 



WM 




Pig. 26. — General Paths of Atmospheric Pressure Transition 3 (see page 65K 

considerable period but are constantly being dissipated and recon- 
structed. After their formation they break away from the main areas 
of maximum pressure and are carried eastward with the general east- 
ward drift of the atmosphere and in their translation become an active 
factor of variable winds. 

39. The Translation of Storm Centers. — On every weather map 
are shown areas of high and low pressure produced by conditions that 
have already been discussed. The low pressure centers are called the 
storm or cyclone centers ; the high pressure centers are called anti- 
cyclone centers, and the winds blow around these centers in the gen- 
eral direction of the hands of a clock but less distinct than in the cy- 
clone (see Fig. 25,* page 63). Inside the area covered by the closed 
isobars of the cyclone, the circulation is upward as well as counter- 
clockwise, while on the area covered by the closed isobars of the anti- 



Translation of Storm Centers. 



65 



cyclone, the atmospheric movement is downward, bringing cold air from 
high altitudes. Between these centers is an atmospheric pressure 
gradient of greater or less magnitude, which causes the air to flow 
from the high areas to the low areas with an intensity depending on 
the difference in pressure between these two centers of atmospheric 
action. 

In addition to the atmospheric movement, there is also a movement 
of these centers on more or less definite paths across the country from.' 
west to east. The anticyclones or high centers enter the country dur- 




Fig. 27. — Divisions of the United States for the Study of Storm Movements 

ing the winter in general from the northwest. In the summer months 
the high areas enter the United States from the Pacific and pass south- 
easterly to Florida or, after entering the country northerly along the 
Columbia River, they follow easterly to the Gulf of St. Lawrence 
From October to March, many areas of high pressure enter the States 
near the one hundred and fifteenth meridian and either follow along 
the mountain slope to the southern route or turn abruptly eastward 
over the lakes to the New England States. The general routes de- 
scribed are shown in Fig. 26, page 64. Storm centers or centers of 
low area are of more general and local origin. The United States 
Weather Bureau has adopted nine districts in its study of the local 
origin of cyclonic storms, and Fig. 27, page 65, shows these districts, 
the number of storms which were first observed therein and the gen- 
Hydrology — 5 



66 Winds and Storms. 

eral direction or path of translation of the storms that formed in each 
district during the ten years' time from 1884 to 1893, inclusive. 

40. Storm Movements. 4 — The points at which storms originate and 
their paths, as previously indicated, vary with the seasons. The origin 
and paths of storm centers, with the number of storms that originated 
in each district for each month of the year during the ten-year period 
from 1884 to 1893, inclusive, are shown by Figs. 28, 29, 30, pages 
67, 68 and 69. The actual daily barometric conditions which ob- 
tained during the passage of certain storm centers for the period of 
March 20-23, 1913, are shown on the four diagrams of Fig. 31, page 
70. These storms originated in the northern Pacific district, passed 
southeasterly through Colorado, thence northeasterly over the Great 
Lake region, leaving the country from the extreme northeast. The 
storm, which was centered over Lake Michigan on March 20, lost its 
force during the following twenty-four hours and was dissipated. The 
storm center, which was centered over the southwestern plateau region 
on the 20th, developed rapidly in intensity and moved northeastward 
across the Great Plain and was centered on the 21st over the Great 
Lakes. It was accompanied by strong shifting gales and widespread 
precipitation, and was followed by a cold wave of unusual severity for 
March. On March 22, this storm had reached the mouth of the St. 
Lawrence, but rain was still falling in the Eastern States. On March 
23 a third widespread storm had moved forward from Nevada to 
Colorado and was moving toward the Great Lake region with increas- 
ing intensity. The above conditions were those which preceded the 
heavy rains of March 23-27, 19 13, which produced abnormal floods 
in the Ohio Valley and the northeastern United States, and the further 
progress of this storm is illustrated- by the four maps shown in Fig. 146. 

41. Local Wind Movements. — As shown by Fig. 23, page 60, the 
United States is in the belt of prevailing southwesterly winds, and the 
general drift of the atmosphere is toward the northeast, as shown by 
Figs. 27 to 30 inclusive. The prevailing winds of any locality may 
however vary greatly from this general direction, and the passage of 
storm centers will in each case give rise to radical variations in the local 
wind direction for the reasons described in Section 38. 

Local winds are greatly modified by local topographic conditions and 
the relative heating of land and water surfaces; they also increase in 



4 See Bulletin No. 20, U. S. Weather Bureau, "Storms, Storm Tracks, and 
Weather Forecasting." 



Storm Movements. 



67 




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68 



Winds and Storms. 













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Storm Movements. 



69 




70 



Winds and Storms. 




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Local Wind Movements. 



71 



intensity, with the elevation above the ground surface and near the 
ground surface with the daily advent of the sun's heat (see Fig. 32, 
page 71). At stations of high elevations and at all high altitudes the 
change in the velocity of the wind with the advent of day is reversed 
from that at stations of low elevation, and the velocities of the wind at 
night exceed those of the day. (See Fig. 33, page 72). The in- 
crease in the wind's velocity with the height above the earth's surface 

0-M. Noon p.m. 

Z 3 A 5 6 7 8 9 /O // 12 / 2 3 A 5 6.78 9 10 1 1 




Fig. 32, 



-Diurnal Variation of the Wind near the Earth's Surface, Atlantic 
City, N. J. 5 



is less where the station is located near level water or prairie surface 
and greatest near broken and forested portions of the country. 

The average hourly velocity of the winds in various parts of the 
United States, estimated for elevation of ioo feet above the ground, is 
shown in Fig. -34, page J2, and the diurnal march of the wind veloci- 
ties near the earth's surface at both low and high altitudes is shown by 
Figs. 32 and 33. 

While the direction of the local winds varies from day to day and 
even from hour to hour, due to the passage of storm centers, certain 



5 Figs. 32 to 36 inclusive are taken from the Year Book, Department of Ag- 
riculture, 1911. See article on The Winds of the United States and their Eco- 
nomic Uses, by P. C. Day, p. 337. 



72 



Winds and Storms. 



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Fig. 33. — Diurnal Variation of the Wind at High Elevation. Pike's Peak, 
Colorado (see page 71). 




Fig. 34. — Average Hourly Velocity of Wind Estimated for Elevation of 100 
feet above Surfaces (see page 71). 



Tornadoes. 73 

prevailing directions are established by the continuous observation of 
the Weather Bureau for each locality. The prevailing direction of the 
local winds of the United States for January and July, respectively is 
shown in Figs. 35 and 36, page 74. From these maps the various 
monsoon effects of changes in temperature of the land and sea, due to 
the season, are well illustrated by the changes in the Eastern States 
from the prevailing northwesterly winds of winter to the prevailing 
southwesterly winds of summer. 

Table 2 gives the average number of storms originating in each dis- 
trict (see Fig. 27, page 65) annually during the period from 1883 to 

1894. 

TABLE 2. 

Number of Storms Originating in Each District During the Years 1SS3-1894 
District 

Average Annual 
Number of Storms 

Northern Pacific 18.4 

Southern Pacific 2.3 

Northern Rocky Mountain 9.9 

Alberta 42.7 

Colorado 12.5 

Texas 10.9 

Central '6.3 

East Gulf 3.0 

South Atlantic 2.9 

West Indies 4.4 

Average Number of Storms per Year 113.3 

42. Tornadoes. — The tornado is more liable to occur in certain parts 
of the United States than in any other portion of the world (see Fig. 
37, page 75). These are storms of the smaller extent and of the most 
violent type, and in proportion to their size are the most disastrous. 
They are limited in extent to a width of from fifty feet to about a 
quarter of a mile and their path seldom exceeds fifty miles in length, 
whereas the great cyclonic storms which are continually passing across 
the country are often a thousand miles or more in diameter and their 
paths can frequently be traced from the Pacific to the Atlantic Ocean. 
The tornado may occur in any month of the year, but is more common 
during the period from March 15 to June 15. 6 They occur during the 
hottest portions of the day and are always associated with violent 

e Moore's Descriptive Meteorology, pages, 237, 238. 



74 



Winds and Storms. 










t I t ^^U^ 

— J t f N K, > \) x -i- 




Fig. 35. — Prevailing Direction of the Surface Winds of the United States in 
Januarys (see page 73). 




Fig. 36. — Prevailing Direction of the Surface Winds of the United States in 

Julys (see page 73). 



Tornadoes. 



75 



thunder storms, heavy precipitation and usually with hail. Tornadoes 
usually form in the southeast quadrant of low pressure cyclonic storms 
during conditions of great humidity and after a morning temperature 
of 6o° to yo°. They are believed to be the result of rapid local heating 
of the lower atmosphere, accentuated by southerly winds which create 
unstable conditions, most frequently resulting in the establishment of 
somewhat local circulation and consequent thunder storms ; but occa- 




Fig. 37. — Geographical Distribution of all Recorded Tornadoes in the United 
States frofn 1794 to 1881 (after Greely — American Weather). 

sionally there is created a limited vertical whirl which develops the 
great vortical energy of the tornado. 

Before the formation of the funnel cloud, which is characteristic 
of the tornado, the clouds have a greenish black appearance and appear 
to rush together with a great violence. The black funnel then appears,, 
drops lower until it reaches the ground surface, when it enlarges some- 
what, rises and sways from side to side and sometimes jumps a space 
and strikes the ground farther on. The destructive effect of the tor- 
nado seems to be occasioned both by the heavy wind pressure and the 
high vacuum which obtains at the storm center and which frequently 
causes walls to fall outward and buildings to explode, apparently from 
the outward pressure of the air within. While the conditions favor- 
able to the formation of tornadoes may be foretold, it is not possible 



76 



Winds and Storms. 



with the present knowledge to forewarn the communities -in the exact 
location where tornadoes may occur without falsely alarming many 
towns within the district which will be entirely free from such visits. 
In general, the country 300 miles southeast from the main cyclonic 
center is in the region of greatest danger. 7 

43. Hurricanes and Typhoons. — Hurricanes and typhoons are more 
limited and more violent cyclonic disturbances than the normal cyclone 




Fig. 38. — Mean Paths of West Indian Hurricanes during different Months 
1876 to 1911. Short arrows indicate tracks of greatest deviation from 
the mean, the numbers are the year of occurrence (after Garriott). (see 
page 78.) 

previously considered and result from a more perfect system of vor- 
tices in the atmosphere. The tornado and water spout are of the same 
character and differ only in more limited dimensions and more intense 
action. Apparently the deflecting force, due to the earth's rotation, is 
essential to the formation of the vortex motion which gives rise to 
cyclones and tornadoes, for no such storms occur in the equatorial 
belt, although convectional action is there most powerful. 

The tropical hurricanes and typhoons, which occur in considerable 
numbers along the polar margin of the equatorial belt, are generated 
at the time this belt has migrated farthest from the geographic equator. 
These storms do not occur far out in the open sea, as the powerful 



Milham's Meteorology, page 236. 



Hurricanes and Typhoons. 



11 




80° SO" 100° 110" 120° 130" 

Fig. 39. — Mean Tracks of East Indian Typhoons s (see page 78). 



140° 



trade winds prevent an invasion of their territory, except near the land 
where the trade winds are weakened by temperature and topographic 
causes. The origin of hurricanes is probably due to the planetary cir- 
culation, modified by the rapid heating of the lower atmosphere, which 
rises and is replaced by a more dense stratum from above. This, under 



s Figs. 39 to 41 inclusive are taken from Cyclones of the Far East by Rev. 
Jos6 Algue\ 



78 



Winds and Storms. 



the proper conditions, causes an intense local circulation which creates 
secondary vortices of the tornado type. In the tropics these follow 
the general westerly motion of the trades, traveling along the margin 
of the belt in which they originate, until a weak condition in the west 
wind zone allows their entry into the regions of western variables. 

Such storms are exemplified by the West Indian Hurricanes (see 
Fig. 38, page j6), and the East Indian Typhoons (see Fig. 39, page 
yy), which occur chiefly in August and September. In the southern 































































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Ian Feb Mar Apr May June July Aug Sept Oct Nov Deo. 

Fig. 40. — Mean Monthly Frequency of Tropical Storms. s 

Atlantic such storms are unknown and they are rare in the southern 
Pacific. 

In the northern Indian Ocean, on account of its relation to the land, 
the planetary system of circulation is greatly modified, but cyclones 
similar in type to the typhoons frequently take place in the Bay of 
Bengal. In the South Indian Ocean, hurricanes of similar origin are 
generated in March and April east of the Island of Madagascar. The 
mean monthly frequency of tropical storms is shown in Fig. 40, and 
the annual occurrence for each year from 1876 to 19 10 is shown by 
Fig. 41, page 79. 

The hurricanes are of greatest interest to the hydraulic engineer 
on account of their influence on rainfall and on harbor and land pro- 
tection in the areas in which they occur. 

44. Hurricane Movements. — In Fig. 38, page 76, are shown the 
mean paths of West Indian hurricanes during different months from 



Hurricane Movements. 



79 



1876 to 191 1. On this map the short arrows represent tracks of storms 
of greatest deviation from the mean and for the year indicated. West 
Indian hurricanes are the most severe of any general storms that visit 
the United States and occasionally, on account of the tremendous 
winds, the heavy precipitation and the high tides and waves which 
accompany their advent into the country, cause great loss of life and 
properly. 

On the night of September 8, 1900, one of these storms of tremen- 
dous force reached the Texas coast near the City of Galveston and 

1876 J878 7880 08Z J884 1886 /S88 1890 /89Z 7894 7896 7898 1900 19QZ 1904 1906 1908 /9/0 




!Fig. 41. — Annual Frequency of Tropical Storms: A — West Indian Hurri- 
cane. B — Cyclones of Bay of Bengal. C — Typhoons of Western Pacifies 
(see page 78). 

caused a loss of over 6,000 lives and of about $30,000,000 in property 
in the City of Galveston alone. About fifteen years later, on August 
17, 1915, a similar storm visited the same locality but with less 
serious results, largely on account of the precautions which had 
been taken after the tragedy of 1900 and the warning of the United 
States Weather Bureau. The loss in this storm, however, amounted 
to about 275 lives and probably more than $5,000,000 in property. In 
the interval of fifteen years between these two great storms no severe 
hurricane visited the Texas coast, except one that passed south of Gal- 
veston on July 21, 1909, which caused severe northerly gales and some 
consequent damages to structures along the shores near Galveston. As 
the tides were low no lives were lost. The path of the storm of 1915 



80 



Winds and Storms. 



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Cold Waves. 



8 



and the barometric conditions which prevailed throughout the United. 
States for the period August 15-21 are shown in Fig. 42, page 80. 
Figure 43, shows the air pressure changes at Galveston and Houston, 
Texas, during this storm. On the map for August 21st are also shown 
the path of the September, 1900, hurricane and the path of the hur- 
ricane of September, 1909, which produced high water conditions near 
the mouth of the Mississippi River and caused a loss of about 350 
lives and a loss of approximately $5,000,000. A similar hurricane also 















































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6 a 10 XII Z 4 6 3 10 M Z 4 6 8 10 XII Z 4 6 8 10 M 8 ° 

Fig. 43. — Barometric Pressures in Inches at Galveston and Houston during 
Hurricane of August, 1915.9 

visited the region of New Orleans on September 29, 1915, and oc- 
casioned a somewhat similar loss of life and property. 

45. Cold Waves. — From the best available data it appears that the 
lowest temperatures in the Northern Hemisphere are found, not at the 
north pole, but in a belt that crosses the Continents between latitude 
50 and 70° north, and that the lowest known temperature, — 90.4 , 
was experienced in Siberia in latitude 6y° 5' north. This cold belt, 
which lies next to the Arctic region on the south, is broken where it 
crosses the water surfaces of Behring Straits and the seas east of 
Greenland, and is also modified by the influence of the eastern atmos- 
pheric drift from the seas over northern Europe and over the western 
region of the American Continent. 

The principal track of high barometric centers in North America 



9 Monthly Weather Review, August, 1915. 
Hydrology — 6 



82 



Winds and Storms. 



lies south of the 50th parallel and their passage disturbs the North 
American cold belt and draws southward masses of cold air that con- 
stitute the cold waves of the United States. These movements some- 
times reduce temperatures to — 40 or even — 6o° in the west part of 
the extreme northern portion of the Central United States, with a min- 
imum of — 63. 1 ° at Popular River, Montana 10 (see Fig. 44). The 
passage of these high areas frequently draws cold air far to the 
southward, and occasionally during a long term of years temperatures 




Fig. 44. — Minimum Temperatures in the United States. 10 

are reduced to the freezing point even as far south as the southern 
lines of Lake Okeechobee in Florida. The barometric changes and 
the temperature effects due to advance of one of these cold waves 
which produces freezing in all of the Gulf States are shown in Fig. 45, 
page 83 11 which shows the temperature and barometric condition for 
each of the four days from December 26 to December 29, 1894. On 
the 29th the temperatures at several points in Southern United States 
were as follows : 

Mobile 16° Jupiter 24° 

Jacksonville 14° Tampa 19° 

Key West 44° 



10 See Bulletin Q, U. S. Dept. Agriculture, Weather Bureau, "Climatology of 
the United States," by A. J. Henry. 

11 See Bulletin P, U. S. Dept. Agriculture Weather Bureau, "Cold Waves 
and Frost in the United States," by E. B. Garriott. 



Cold Waves. 



83 




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84 Winds and Storms. 

46. Hot Waves. — The movements of barometric pressure centers as 
indicated in Fig. 26, page 64, represent average conditions from 
which great variations sometimes obtain. During the summer season 
periods of stagnation occur in the movements of these centers. When 
at such times a center of high pressure rests over the southern Atlantic 
Ocean, with low centers over the northern Rocky Mountain region 
or along the northern border of the United States, the pressure dis- 
tribution will normally produce high temperature conditions in the 
Mississippi Valley and the Atlantic States due to the southerly winds 
which cause a continuing flow of heated air from the Gulf of Mexico 
and Southern Atlantic over these regions. The series of maps, Fig. 
46, page 85, show the conditions for July 1-4, 1901, and illustrate 
the pressure, temperature and wind conditions during an extreme hot 
weather period. It may be noted that at 8 A. M. on July 2, 190 1, the 
thermometer stood at 92 in Philadelphia, 90 in Baltimore and 88° 
in New York City. Figure 47, page 86, shows the maximum recorded 
temperature in the United States. 12 

47. Hydrological Effects of the Winds. — A study of the character 
of the winds which occur in any locality is of importance to the hy- 
draulic engineer on account of their effect on both precipitation and 
water levels. These atmospheric movements transfer such vapor as 
may be taken up from bodies of water, moist earth areas or areas of 
vegetation and deposit them again wherever the conditions are favor- 
able for precipitation. The passage of atmospheric currents that have 
been relieved of their moisture, on the other hand produces evapora- 
tion and adds to aridity. Hence the normal and possible movement 
and paths of cyclonic storms and the resulting direction of the wind, 
together with the character of the surface over which the winds have 
passed, materially affect their rain bearing qualities. These conditions 
will be further considered in future chapters, as will also the subject 
of normal stream flow and the occasional extreme flood conditions 
to which they give rise. 

The direct effects of the passage of storm centers on the elevation of 
surface waters by wind tides and storm waves are also important mat- 
ters to engineers in charge of construction on or in the immediate 
vicinity of large bodies of water and will be considered in the next 
chapter. 



12 See Bulletin Q, U. S. Weather Bureau, "Climatology of the United States," 
by A. J. Henry. 



Hot Waves. 



85 



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86 



Winds and Storms. 



48. Weather Forecasting. — The study of the preceding sections of 
this Chapter should give a fairly good idea of the basis of weather 
forecasting. The data from which the daily weather map is made 
are taken each morning at 8 o'clock, 75th meridian time, which is ap- 
proximately equal to 7 o'clock at Chicago, 6 o'clock at Denver and 5 
o'clock at San Francisco. The various observers at some 200 stations 
in the United States and the West Indies, after taking the observa- 
tions for air pressures, temperatures, humidity, precipitation, wind 




Fig. 47. — Maximum Temperatures in the United States is (see page 84). 

direction and cloudiness, send these observations to Washington. Cer- 
tain important stations also receive observations from such other sta- 
tions as are required for local forecasting. In the Forecast Division 
at Washington, these data are assembled on various charts, including 
charts showing : 

1st. Changes in temperatures during the preceding twenty-four 
hours. 

2d. Changes in barometric pressure. 

3d. Humidity of the air. 

4th. Cloud areas. 

5th. Air temperatures and pressure, velocity and direction of the 
wind, character and amount of precipitation since last reports, and 
cloudiness. 



13 TJ. S. Weather Bureau Bui. Q, by A. J. Henry. 



Weather Forecasting. 87 

On this chart, which is the general weather map familiar to the pub- 
lic,- isobars and isotherms are drawn, the former indicating the centers 
from and toward which the air movements must take place. 

From years of experience the forecaster knows : 

i st. That high and low pressure areas drift across the country from 
the west toward the east in periods averaging from three to four days 
each and at a speed of about 600 miles per day. The average speed 
of movement is about thirty-five miles per hour in winter and twenty- 
four miles per hour in summer, for the lows, and about thirty miles per 
hour in winter and twenty-two miles per hour in summer, for the highs. 

2d. That the lows, as they drift east, bring warmer weather and often 
rain or snow, while the highs which follow will bring cooler and prob- 
ably fair weather. 

3d. That occasionally there are periods of stagnation in the drift 
of the high and low areas, and that at such times there occur abnor- 
mal conditions of cold, heat or precipitation. 

4th. That about forty per cent, of the storms come from the north- 
west and pass easterly over the Lakes and New England, usually pro- 
ducing but scanty rainfall. 

5th. That about twenty-one per cent, of the storms come from the 
arid regions of the southwestern states and in their northeastward 
movement can usually be depended upon to produce considerable rain. 

6th. That the most severe general cyclonic wind and rain storms in 
the United States originate in the West Indies, travel in a northwest- 
erly direction until they reach the South Atlantic or Gulf Coast, and 
then recurve to the northeast and sweep along or approximately paral- 
lel the Atlantic Coast, their path being determined by the position and 
intensity of pressure centers to the north. 

7th. That under the known conditions that exist at the time of ob- 
servation the storm movements will in general follow well established 
paths and give rise to conditions in the next twenty-four hours that 
are fairly determinate. 

8th. That at times accelerating forces, not indicated by the daily 
observations which are taken only at the bottom of the great air mass, 
develop unexpected energy, cause the pressure centers to pursue paths 
not previously indicated, or gradually dissipate the energy of the 
storm in a manner not foreseen in the previous daily forecast. 

After the data are duly correlated on the weather map, the fore- 



88 Winds and Storms. 

caster notes the changes and movements in the air conditions during 
the preceding twenty-four hours, and from these data he estimates 
what the weather will be in the different sections of the country the 
following day. 

LITERATURE 

A Popular Treatise on the Winds, Wm. A. Ferrel, 1899. 

The Weather and Practical Methods of Forecasting It, E. B. Dunn, Dodd, 
Mead & Co., 1902. 

American Weather, A. W. Greely, Dodd, Mead & Co., Philadelphia, 1888. 

Annual Reports, U. S. Weather Bureau. 

Monthly Weather Review, U. S. Weather Bureau. 

Storms, Storm Tracks and Weather Forecasting, Frank H. Bigelow. Bulle- 
tin 20, U. S. Weather Bureau, 1897. 

Cyclones of the Far East, Rev. Jose Algu6, S. J. U. S. Weather Bureau, 1904. 

Climatology of the United States, A. J. Henry. U. S. Weather Bureau, 1906. 

Cold Waves and Frosts in the United States, E. B. Garriott. U. S. Weather 
Bureau, 1906. 

West Indian Hurricanes, E. B. Garriott. U. S. Weather Bureau, Bulletin H, 
1900. 

Hurricanes of the West Indies, Oliver L. Fassig. U. S. Weather Bureau, Bul- 
letin X, 1913. 

Cause of Trade Winds, F. A. Velschow, Trans. Am. Soc. C. E. Vol. 23, 1890, 
p. 106. Presents views at variance with usual accepted theory. 



CHAPTER V 

HYDROGRAPHY 

49. Ocean Currents. — The circulation of the water of the ocean is 
caused by the heating at the tropics and cooling at the poles, which 
induces a general surface motion poleward and a motion in the depth 
toward the equator which is more or less modified by the continental 
masses and irregularities and by the difference in the velocity of rota- 
tion of the earth at the equator and the poles. The results of these 
causes are ocean currents more or less restricted in the limits of their 
surface activity (see Fig. 48, page 91). 

The ocean currents have an indirect effect on the temperature and 
rainfall of the various land areas eastward of the courses in which 
they flow. The warm ocean currents on their poleward flow increase 
the temperature of the superincumbent atmosphere which in drifting 
eastward, warms the northwestern shores of the continents. As the 
cold returning currents wash the eastern shores they can have practically 
little effect on those shores, except through their modification of the tem- 
perature of occasional ocean breezes. The modifying effect on the land 
temperatures of the eastward drift of the atmosphere from the ocean to 
the land is well illustrated by Figs. 15 and 18, pages 50 and 52, showing 
the isothermal lines of the Northern Hemisphere for January and July, 
respectively. The lines on the west coast of both Europe and North 
America are carried northward, while those of the eastern shores of Asia 
and North America are carried southward. The latter effect, however, 
is not due to the cold ocean currents but is a result of normal continental 
temperatures, the effects of which are in fact extended far to the east- 
ward over the oceans by the normal atmospheric drift. 

The effect of the ocean currents is less marked in the Southern 
Hemisphere due to the greater amount of water area and the conse- 
quent greater regularity in the courses of the currents and to the fact 
that the greater water area tends toward a more uniform distribution 
of heat. 

50. Lake Currents. — Various factors will create currents more or 
less distinct in inland lakes. Among these are : 

1. The general trend of the waters toward the outlet. 

2. The inflow of water from streams. 



90 Hydrography. 

3. The winds. 

4. Variations in air (barometric) pressures on different portions of 
the lake. 

5. Variation in temperature at different depths. 
■ These factors normally result in : 

a. A main current toward the outlet. 

b. Surface currents due to wind and barometric gradients. 

c. Return currents due to the escape of water temporarily banked up 
by winds or by air pressure. 

d. Vertical currents caused by temperature changes. 

In general, the body of water of a lake is so large relative to its out- 
flow that the main lake currents are often obscured or reversed by 
winds and barometric effects. These currents are seldom so persistent 
and intense as to "assure the continuous passage of water, with any 
material it may carry, in a single direction although under certain cir- 
cumstances such conditions may obtain for the greater part of the time. 
The subject of lake currents is of particular interest and importance 
in the study of the distribution of polluted waters from rivers or sewers 
relative to water supply intakes from the same bodies into which such 
polluted waters are discharged. 

51. Vertical Lake Currents.- — In temperate climates, except during 
the period when lakes are ice covered, the temperature of the surface 
waters varies with the mean atmospheric temperature. From the 
breaking up of the ice in the spring, the surface waters begin to increase 
in temperature until about midsummer, after which they begin to cool 
until they reach 32 ° : Fahrenheit in the fall with the freezing of the sur- 
face. On account of the greater density of water at 39. i° Fahren- 
heit, when the temperature of the* surface water reaches that stage it 
begins to sink allowing warmer or colder water to take it's place until 
there is an adjustment of the whole body of water in accordance with 
its density and so far as it can be affected by changes in density. In 
shallow lakes less than 20 feet in depth, this vertical circulation of water 
is continuous except when the surface is frozen. In large and deep 
lakes there is but little vertical circulation as water of maximum density 
rests on the bottom at all times. In lakes of intermediate depth there 
are two periods of vertical circulation namely in the spring and in the 
fall when the surface temperature changes through that of maximum 
density and also two periods of stagnation, namely during the summer 
and winter periods. This circulation is of importance relative to the 



Lake Currents. 




92 Hydrography. 

temperature and quality of water supplies which are affected by these 
periods of circulation and stagnation.* 

52. Tides. — A periodical movement of the sea water which is not 
primarily circulatory is caused by the attraction of the sun and moon. 
This movement, which is manifested as a progressive wave called the 
tide, takes place essentially simultaneously on opposite sides of the 
earth. The effect of the sun is about forty per cent, of that of the 
moon. Due to the difference in the differential attraction of those two 
bodies, when the sun and moon act together upon one portion of the 
earth's surface, the high or spring tides occur and the low or neap 
tides result from the sun and moon acting in opposition, each condi- 
tion taking place twice in each lunar month. The problems and con- 
ditions presented by the tides are of importance in many affairs, such 
as improvement of harbors and other coast work, determination of 
mean sea level datum, determination of the mass of the moon, rigidity 
of the earth and other geodetic research. 

The investigation of the problem of the tides is exceedingly com- 
plex, since the influence of many conditions must be considered. Thus 
the height and speed of progression of the tidal wave are affected by 
the laws of wave motion, and attraction and motion of the moon, the 
attraction of the sun, the rotation and revolution of the earth, the in- 
ertia of the mass of water, the viscosity of the water, the friction of 
the water against the bottom, the irregularity of contour of the bottom, 
the interference and reflection of the wave due to the irregular land 
masses and other conditions. 

According to the law of wave motion as shown by Prof. G. B. Airy, 
the speed of progression of the wave depends directly upon the depth 
of water when the length of wave fr.om crest to crest is large in com- 
parison with the depth, and is the same as that which a free body 
would acquire by falling from rest through a height equal to half the 
depth of water. This law is mathematically expressed as 

(l) v=vFd 

where 

v represents the velocity of propagation 

g represents the acceleration due to gravity 

d represents the depth of water 

The wave can theoretically progress in synchronism with the ap- 
parent motion of the moon only when the depth is more than thirteen 



*See Miscroscopy of Drinking Water, by G. C. Whipple, Chap. V; also The 
Temperature of Lakes, by Desmond Fitzgerald. 



Tid 



es. 



93 



or fourteen miles, and since there are no such depths in the ocean the 
wave is forced to lag behind the point which is under direct attraction 
of the moon because of friction on the bottom of the sea. This lag 
is further augmented by the inertia and viscosity of the water itself. 

Considering the great variability in contour of the bottom and the 
consequent changes in the amount of friction, it is easily understood 
that unknown and very complex factors are introduced into the prob- 
lem, and the influences are rendered still more complicated by the 
land masses which interrupt and reflect the wave. 




Fig. 49. — Range of Spring Tides in and near the Bay of Fundy. 

In the open ocean, the tidal wave is three or four feet in height. As 
a wave passes from deeper to shallower water, the increased friction 
tends to decrease the height of the wave, while the expenditure of the 
same amount of energy on the small mass of water conduces to in- 
crease the height, the total result being to produce a higher wave. 
Under favorable conditions, the increase in height is very pronounced. 
Perhaps the best example of the great range in tides caused by the 
peculiar relation and configuration of the land and the increase toward 
the head of an inclosed body of water is found in the Bay of Fundy. 

Figure 49, shows the range of the spring tides along the coast of 
Nova Scotia and the State of Maine, and the increased height toward 
the head of the Bay of Fundy, where an extreme of 50.5 feet is reached 
in Noel Bay, Minas Basin. 



94 Hydrography. 

In the Gulf of California the rise of spring tides is about six feet 
at Alata near the mouth and thirty-one feet at the mouth of the Colo- 
rado River at the head of the Gulf. 

"In Bristol channel the rise of spring tides at the mouth is about 
eighteen feet, at Swansea about thirty feet, and at Chepstow about 
fifty feet." x 

Under certain circumstances, obstructions at the mouth of an estuary 
present a condition causing the tide to enter as one or more waves, 




Fig. 50. — Hangchow Bore at Harming on the Tsien-tang River, China.2 

known as the eagre or bore. Examples of this state are furnished by 
the Amazon River, which the bore ascends in three great waves 
thirteen to twenty-three feet in height. Figure 50, from a photo- 
graph, shows the bore in the Tsien-tang River at Harming, . taken in 
19 14. The crest of water was vertical and about sixteen feet in height, 
with a second wave four feet in height so close behind that it cannot 
be distinguished in the picture. The river at Harming is about a mile 
in width and the water continued to rise for thirty minutes after the 
crest had passed, finally reaching a height of twenty-eight feet. The 
wave traveled with a high velocity. In seven minutes after it could be 
distinguished on the horizon the wave had passed. 2 Thus it is seen 



1 See Professional Paper No. 31, Corps of Engineers, U. S. A., p. 90. 

2 Photograph and data furnished by Mr. E. C. Stocker of Shanghai, China. 



Tides. 



95 




96 Hydrography. 

that the height- and amplitude, as well as the speed of progression of 
the tidal wave, are subject to great variations and complications, be- 
cause of the many complex influences exerted by the great variety of 
existing conditions. These complications are so great as to prevent a. 
general solution of the problem of the progress of the tide. 

At any certain place the height and occurrence of the tides are pre- 
dicted with a considerable degree of accuracy after the data of ob- 
servations for a year or more have been collected and correlated. The 
accuracy of such predictions becomes more nearly exact as the more 
or less local influences of winds, configuration, etc., become of rela- 
tively less moment and the transit of the sun and moon bear more di- 
rectly upon the time of occurrence. The . computations entailed in- 
predicting the tides are now accomplished by a complicated mechanical 
device known as the tide predicting machine, the latest one of which 
provides for thirty-seven components. 3 

Fig. 51, page 95, is a map reproduced from an article on "CotidaL 
Lines for the World," by R. A. Harris. 4 The lines on the map are sup- 
posed to represent the lines of simultaneous high water at each hour 
Greenwich time. Mr. Harris says : 

"It will be noticed that there are several points from which the cotidal 
lines for all hours seem to radiate, and so must be points where the 
range of tide is zero. These points and radiating lines are caused by 
the overlapping of systems, by progression due to secondary or de- 
pendent bodies of water into which a free wave progresses, and by the 
necessity of a gradual change between adjacent regions whose tides 
are not simpultaneous. * * * 

"It has been supposed that the tides of the ocean advanced westward 
around the globe, endeavoring to 'follow the moon in her apparent 
diurnal course in the heavens. A westerly progression was especially 
looked for in the southern areas where a continuous zone of water en- 
circles the earth. What have we in reality? A remarkable eastward 
progression in the Pacific Ocean due to the opening between Cape Horn 
and Graham Land forming a break in the rigid boundary which con- 
stitutes the eastern support of the South Pacific oscillating system." 

It is probably true that the tidal motion of the water in ocean basins 
is an eastward and westward swinging motion rather than a series of 
progressive waves as seems to be indicated by the map. 



3 U. S. Coast and Geodetic Survey Tide Predicting Machine No. 2, by E. G.. 
Fischer, Eng. News, July 20, 1911. 

4 National Geographic Magazine, Vol. 17, p. 303, June, 1906. 



Tides. 97 

Numerous other examples of the profound effect of continental 
configuration upon the progression or height of the tidal waves exist ' y 
among some of the most striking may be noted the case of New York 
Bay. The high tide at the western end of Long Island is some three 
hours later than that at Governor's Island in New York Harbor. This 
condition is produced by two waves, one of which progresses around 
the eastern end of Long Island and the other up East River. The 
meeting of these waves produces such an effect that the time of high 
tide differs by as much as an hour for points within a mile of each 
other. 

Another case of complication is that of Lynn Canal, Alaska, near 
Sitka. This canal is about ioo miles in length and extends in a north- 
ward direction. The time of high tide occurs at the upper end at 
about the same time as that at the mouth. This occurrence is attrib- 
uted to reflection of the wave from the inner end. 

Table 3 gives the range in spring and neap tides at various impor- 
tant points throughout the world. 

TABLE 3. 

Tide Table. 

Range of Tides. 

AMERICA Spring. Neap. 

St. J ohns, Newfoundland 3.3 1.5 

Halifax, Nova Scotia 5.2 3.2 

Pubnico, Mouth, Bay of Fundy 12.0 8.9 

Noel Bay, Minas Basin Head, Bay of Fundy 50.5 37.4 

Rockland, Mouth, Penobscot Bay 11.0 8.2 

Bucksport, Penobscot River 12.5 9.4 

Bangor, Penobscot River 14.9 11.1 

Boston, Navy Yard 10.9 8.1 

Pleasant Bay, Cape Cod 4.1 2.9 

New York, The Battery 5.3 3.4 

Philadelphia, Pennsylvania 5.6 4.9 

Washington, D. C 3.3 2.4 

Old Point Comfort, Virginia 3.0 2.6 

Cape Hatteras, North Carolina. 4.2 3.1 

Miami, Key, Biscayne Bay, Fla 1.3 0.9 

Key West, Florida 1.6 0.9 

Tampa, Florida 2.9 1.4 

Port Eads, Louisiana .2 .1 

Galveston, Texas 7 .4 

Havana, Cuba 1.3 0.7 

Colon, Panama 1.1 0.6 

Balboa, Panama 16.2 8.7 

Maraca Island, Brazil 30.0 14.3 

Entrance, Amazon River, Brazil , 14.3 6.8 

Altata, Mouth, Gulf California 5.8 1.4 

Hydrology — 7 



98 Hydrography. 

TABLE Z.—Tide Table— Continued. 

Range of Tides. 

Spring. Neap. 

Mouth, Colorado River, Head, Gulf California 31.5 7.3 

San Diego, California 5.2 2.3 

San Francisco, California (Presidio) 4.9 3.1 

Columbia River, Bar 7.6 4.4 

Seattle, Elliott Bay 9.1 5.9 

ASIA 

Nagasaki, Japan 8.4 3.4 

Yokohama, Japan 4.8 1.9 

Shanghai, China, Wusung Bar 9.2 4.9 

Hangchow Bay, China 13.7 7.2 

Amoy, China 15.6 9.8 

Hong Kong, China 4.4 2.1 

Bombay, India 14.2 11.2 

EUROPE 

Aberdeen, Great Britain 12. 10. 

Avonmouth, Great Britain 38. 28. 

Belfast, Great Britain 9.5 7.5 

Bristol, Great Britain 33. 23. 

Cardiff, Great Britain 36.5 27. 

Cork, Great Britain 12.7 10. 

Dover, Great Britain 18.7 15. 

Glasgow, Great Britain 12.2 9.2 

Hull, Great Britain 20.7 16.2 

Liverpool, Great Britain 27.5 20.2 

London, Great Britain 20.7 17.2 

Queenstown, Great Britain 11.7 9. 

Southhampton, Great Britain 13. 9.5 

Bordeaux, France 15.5 12. 

Calais, France 21. 17.5 

Antwerp, Belgium 16.7 

Rotterdam, Holland 7. 

Hamburg, Germany 6.2 5.5 

Christiana, Norway 1.5 

Gibralter 3.2 2.5 

MISCELLANEOUS 

Alexandria, Egypt 1. .3 

Zanzibar, Africa «. 15. 10. 

Natal, Africa 6.5 3.7 

Honolulu, Hawaiian Island 1.5 0.8 

• Manila, River Entrance, P. 1 1.8 0.9 

53. Wind Tides. — The directions and intensities of the winds 
have an important influence on tides, waves and consequent water ele- 
vations. The effects of easterly and westerly winds on the surface of 
Lake Erie, the longitudinal extension of which lies in the direction of 
the easterly path of storm centers (see Fig. 52, page 99) is to produce 
at times great variation in the surface elevation at the easterly and 
westerly ends of the lake (see Fig. 53, page 100) . 5 The intense winds 



s Bulletin J, U. S. Weather Bureau, "Wind Velocities and Fluctuations of 
Water Level on Lake Erie," by Prof. A. J. Henry. 



Wind Tides. 



99 



known as hurricanes and typhoons that occur in the West and East 
Indies, respectively, occasionally greatly endanger the safety of cities 
and farm lands which are exposed to such effects. The effects of the 
West India hurricane of 1909 on the elevation of the water surface 
in the lakes and bayous of southern Louisiana near the mouth of the 
Mississippi River are shown on Fig. 54, page 101. 

Much of the loss of life and property in the hurricanes of Sep- 
tember, 1900, and of August, 1915, at Galveston (see Fig. 42, page 
80), and along the coast of Texas, was due to the high wind tides 




Fig. 52. — Map of Lake Erie. 

that were caused by the passage of these storms. The tremendous 
direct attack of the waves accompanying these high tides can be re- 
sisted only by the strongest class of masonry construction. The high 
waters in the interior rivers, bayou and lakes can often be overcome by 
levee construction, properly protected at points exposed to wave wash. 

In the storm of November 21, 1900, the wind at Buffalo attained 
a maximum velocity of 80 miles per hour and the lake level rose to 120 
inches above zero while at Amherstburg, Ontario, near the western end 
of the lake, the water level reached a stage 33 inches below zero. 

54. Seiches. 6 — Seiches are oscillations of the water surfaces of 
lakes above and below mean lake level. They have an amplitude of 
from a few inches to occasionally several feet, and are supposed to be 
occasioned by changes in barometric pressure. Small rythmic oscilla- 

s See Notes on the Hydrology of the Great Lakes, by P. Vedel ; vol. 1, Jour. 
Western Society of Engineers, p. 426 et seq. ; see also Enc. Brit, article on 
lakes. 



00 



Hydrography. 



tions of a few inches in amplitude frequently occur on Lake Superior 
within a period of about ten minutes ; on Lake Michigan similar oscilla- 
tions from the east to the west, with a period of about fifteen minutes, 
are frequently observed. The periods of these oscillations are too 
short for transition from shore to shore across the lake basins, but oscil- 
lations of longer periods and of greater amplitude have been observed 

72 




4-8/2 4 8 12 4 8 12 4 8 12 4 8/248/24 8/24 8/24- 8/24-8/2 Hour 
A/or 19 20 21 22 23 Day 

Fig. 53. — Wind Velocities and Water Level Fluctuations on Lake Erie, No- 
vember, 1900 (From Bui. J, U. S. Weather Bureau) (see page 99). 

between Milwaukee and Grand Haven where such oscillations have oc- 
curred eleven times in twenty-four hours. 7 These oscillations were 
extensively studied early in the nineteenth century in connection with 
the Swiss lakes. 8 

Seiches of unusual height have occasionally been observed. One 
seiche was observed in Lake Geneva in October, 1841, which was seven 
feet high, and in Lake Superior, in I854, a seiche of unusual height was 
said to have left the St. Mary River nearly dry for about an hour. 

On August 16, 1886, a similar series of oscillations occurred in Lake 
Michigan, caused by an area of low pressure passing over the lake and 
continued for about 24 hours. An automatic gage record of the varia- 



1 See Annual Report Chief of Engineers, U. S. A. 1872. 
s See Nature, p. 18, 1878. 




GUI.? 



Fig. 54. — Hurricane Tide Effects in Southern Louisiana, 1900 (from a map by 
Mr, A. M. Shaw, published by the U. S. Dept. of Agriculture) (see page 99). 



02 



Hydrography. 



tions in the lake level at Chicago on this elate was published in the report 
of the Survey of the Waterway from Lake Michigan to the Illinois 
River by Major Marshall. The curve shows regular 15 to 20 minutes 
oscillations the amplitudes of which are a few inches, but combined with 
these oscillations are others of a larger amplitude with a period of about 
40 minutes. Twenty-six waves occurred in an 18 hour period, the 
greatest waves having an amplitude of two feet ten inches, the surface 
falling this distance in 15 minutes. The largest seiche in Lake Mich- 
igan occurred on April 7, 1893, and was noted simultaneously at Chi- 
cago and St. Joe, Michigan, rising to heights of from four to six feet. 

Fig. 55, 9 is the record of an automatic U. S. L. S. gage located 
at the head of the St. Clair River and at the outlet of Lake Huron, 




Datum Line ^Elevation 57767 feet above mean tide at New YorK. 

Fig. 55. — Seiches on Lake Huron. 

and illustrates the occurrence of seiches caused by barometric pressure 
changes on the southern end of Lake Huron. 

55. Waves. — On account of the characteristics of mobility and vis- 
cosity a disturbance to any one of the particles of a body of water is 
transmitted to contiguous particles and thence to others more remote, 
causing ripples, oscillatory movements or movements of translation 
known as waves. The wave is a disturbance of the surface in the 
form of a ridge or depression and is propagated by certain forces 
which tend to restore surface equilibrium. In general the particles of 
water do not advance materially with the wave. 

Ripples are the smallest class of waves in which the surface ten- 
sion of the water is the principal motive force of restoration of the 
particles. 

Oscillatory waves are similar to ripples, except that the motive force 
of restoration is principally due to gravity. These waves always occur 



9 From Report on the North and Northwestern Lakes, by Col. G. J. Lydecker. 
Appendix 111, Report of Chief of Engineers U. S. A. for 1900. 



Wave Motion. 1 03 

in groups and are raised partly above and are partly depressed below 
the undisturbed water level. 

Waves of translation are wholly raised above or depressed below 
the undisturbed water level. Those raised above the general level are 
termed positive waves and those depressed below this level are termed 
negative waves. Such waves are propagated as a single hump or hol- 
low passing over the still water surface. In this wave there is not 
only a progressive movement of the wave form, but also a translation 
of the particles of water for a short distance in the direction of motion. 

Waves may be classified as wind waves, tidal waves or those produced 
by sudden disturbances, such as by earthquakes. The great waves 
sometimes caused by earthquakes are the most serious in the'ir destruc- 
tive effects but are too uncertain in their occurrence, extent and action 
to admit of investigation. 

56. Wave Motion. — A ship at sea which encounters great waves 
moving at a high velocity across its course is not appreciably moved 
from its course but simply rises as the wave crest passes and then 
sinks in the trough which follows. Floating objects near the land 
rise and fall in the same manner as the wave passes, move in or out 
with the tide, or in the direction of local currents, showing that wave 
motion is quite different from the motion of the water in which it 
moves. 

"If a body floating upon the surface of the water be observed care- 
fully, it will be seen to rise, move forward, and sink when on the upper 
portion of the wave, and to continue to sink, move backward, and rise 
again when on the lower portion of the wave, but without appreciable 
movement in the direction of wave travel, except such as may be due 
to the action of wind or of currents. Each particle moves about its 
position of rest in a closed orbit, in a manner consistent with the move- 
ment of all other particles in the wave. How this is accomplished is 
shown in Figs. 56 and 57, page 104, which are modifications of Webers* 
diagram of an oscillatory wave; the particles moving in circular orbits 
in the same direction as the hands of a clock, and the wave advancing 
in the direction shown by the arrow, a, b, c, d, e, f, g, h, etc., Fig. 57, 
represent horizontal, and k, I, in, n, 0, p, a, etc., vertical filaments of 
water' in a state of rest. The positions of the corresponding filaments 
during the passage of a wave are shown in Fig. 56. In this figure the 
filament a is represented by the common cycloid, and all other hori- 
zontal filaments by prolate cycloids. The dimensions of the orbits of 
the particles decrease rapidly below the surface, as indicated by the 
limiting lines rx and rzv in the figure. 



304 



Hydrography. 



"Those particles which lie in the same vertical filament when at 
rest, arrive at the lowest point of their orbits at the same instant when 
wave motion is in progress, taking the position shown at q. When 
the wave advances, the filament takes successively the positions p, o, 
n, etc., the upper portion bending over toward the wave crest until at 
k, directly under the crest, it becomes vertical. After the crest has 
passed, the filament again inclines toward it until the next succeeding 
trough arrives, when it again becomes vertical. 




Fig. 56 



Fig. 57. 



Wave Action. io 



'""When the wave occupies the position shown in Fig. 56, all parti- 
cles between the filaments xx' and nn f have motion in the direction of 
wave travel, and those between nn' and ii f in the contrary direction." 

"Shallow water waves" are those that occur in water of a depth 
less than half the wave length. In such waves the orbits of its par- 
ticles are elliptical instead of circular. In very shallow water the 
rellipse approaches a straight line in form." 10 

57. Height of Oscillating Waves. — The height of a wave is the 
•vertical distance from its highest to its lowest point. Oscillating waves 
will attain their maximum only in waters of adequate depth and no 
-such wave will reach a height greater than the depth of water through 
which it passes. Mr. Thomas Stevenson established from numerous 
•observations a formula for the height of wave in feet relative to the 
"fetch" or distance in nautical miles 11 to the windward shore as fol- 
lows : 

(2) h = 1.5vT 

^vhere h = height in feet 

/ = fetch in nautical miles. 



10 See Professional Paper No. 31, Corps of Engineers, U. S. A., by Capt. D. D. 
Ctaillard. 

11 The nautical mile = 6,080 feet = 1.15 statute miles. 



Height of Waves. 105 

It is .evident that the maximum storms may not come from the di- 
rection having the maximum fetch and that, therefore, calculations 
based on the maximum fetch are often greater than will be realized. 
It must also be noted that heavy rollers as they approach a shore are 
deflected by the retardation due to shallowing water and become more 
nearly parallel with the shore or even change their direction entirely 
through the influence of islands or headlands. 

As the height of waves seldom exceeds forty-five feet, there is evi- 
dently a limit to the influence of the fetch, which in this case would 
correspond to 900 miles, while the width of the ocean may be several 
thousand miles. From the previous chapter it is evident, however, 
that, as most ocean winds have a rotary direction, it is seldom that 
violent winds follow approximately a straight course of more than 900 
miles. 

For short distances (of perhaps two miles or less) and violent 
squalls, Stevenson proposes the formula 

(3) h = 1.5Vf + (2.5 — v'fT 

Hawksley 12 determined by observation that the height of waves in 
feet, h produced in large reservoirs by the heaviest gales in England 
could be represented by a formula that reduces to 

(4) h = .025Vl 
where / = the fetch in feet, or 

(4a) h = 1.95Vf 

58. Length and Velocity of Oscillating Waves. — The length of 
waves seems to be related to the fetch, but is independent of the wave 
height. Waves in the Atlantic are said to be 500 to 600 feet between 
crests, and in the Pacific occasionally reach 1,000 feet. Lieutenant 
Paris of the French navy found the ratio of length to height of 

wave -j— was on an average 39 in light seas, 21 in rough seas and 19 in 
heavy seas. 

In deep water the velocity of the wave is independent of the depth 
and is essentially equal to that acquired by a body falling through a 
height eight per cent, of the wave length and is given by the formula 13 

/gl 

(5) v= / = V5.121 = 2.26V1 

V 2tt 
Rankine states that in shallow water (i. e., water of a depth less than 
one-half the wave length) the velocity is equal to that of a body falling 



12 Proceedings Inst. C. E., Vol. XX, page 361. 
is See "Wave Action" by Gaillard. 



06 



Hydrography. 



through a height equal to half the depth d of water plus three-fourths 
of the wave height h and is given by the formula 13 



(6) 



v= /2g|— H 
V \2 



(d 3h\ 



= 4.012 V 2d + 3h 



Gaillard found this formula to give results considerably in excess 
of the observed velocities. 

The agreement of the calculated with the observed height of waves 
is shown by Table 4. It should be noted that the storm observed may 
not have been the maximum storm which might be expected, hence the 
observed height may not be a maximum. 

TABLE 4. 
Comparative Observed and Calculated Wave Height. ™- u 
Fetch in 



Location. 



nautical 
miles. 

.375 
.428 
.641 
.748 
.916 
. 1.086 

1.3 

1.923 



Observed 
height. 

1.5 

2.3 

2.0 

3.8 

2.0 

3.0 

1.8 

4.5 
11. 

7.0 
15.0 
16.5 
23.0 

4.0 

8.2 
15.0 
22.6 



Calculated height by 

formula. 

(2) (3) (4) 

2.6 1.2 

2.7 1.3 

2.8 1.6 

2.9 1.7 
2.9 1.9 
3.1 2.0 
3.0 2.2 
3.4 2.7 

9.7 

5.0 
16.2 
13.6 
24.1 

4.5 

8.2 
19.3 
30.0 



*Duluth Basin 

*Duluth Basin 

*Duluth Basin 

*Duluth Basin 

*St. Louis Bay 

*Portage Lake 

Firth of Forth 

*St. Louis Bay 

*Stannard Rock 41.45 

San Pedro Bay, Cal 15.64 

Marquette, Mich 116.63 

*Portage Break Water 82.50 

*Duluth Canal 258.62 

Clyde 9.0 

Lake Geneva 30.0 

Sunderland 165.0 

Petershead 400.0 

*Lake Superior. 

Cunningham also gives the following as the recorded height of waves 
in heavy storms : 

Lake Geneva 10 feet 

German Ocean 12 to 15 feet 

Mediterranean Sea 15 to 20 feet 

Bay of Biscay 25 to 30 feet 

Atlantic Ocean 30 to 40 feet 

Pacific Ocean* 50 to 60 feet 

* Off Cape Horn and Cape of Good Hope. 

A wave encountering a current in the opposite direction is increased 
in height ; so also is a wave advancing in a channel either of uniform 
depth and decreasing width or of uniform width and decreasing depth. 
The effect of decreasing breadth and depth is well illustrated by the 



1* See "Harbor Engineering" by Cunningham. 



Oscillating Waves. 1 07 

increase in the tide wave in bays and channels like the Bay of Fundy 
or the Gulf of California, where the rise in tide at the head is several 
times greater than the rise at the mouth. 

When a wave travels from deep water into water the depth of which 
is gradually decreasing, a change in form takes place. Due to fric- 
tion upon the bottom, the velocity and length of the wave decreases, 
while the wave height for a time increases. The front of the wave be- 
comes gradually steeper and the velocity of its lower portion decreases 
until the greater velocity of the particles at the crest carries them 
forward, and the crest falls over, breaking into a foaming mass of 
water. In such cases the wave is transformed from a purely oscil- 
latory to a wave of translation, and the forward motion of the parti- 
cles is equal to the velocity of the wave. Under these conditions the 
wave exerts its maximum power. 

The height reached by waves breaking against headlands and struc- 
tural or protecting works rises by impact to much greater heights than 
those estimated above. Cunningham gives the following observations 
on such waves : 

The Hague 75 feet 

Bell Rock 100 feet 

Eddystone Lighthouse 150 feet 

S. W. Coast of Ireland 150 feet 

The element of waves, often of greatest importance in connection 
with engineering works along the oceans and lakes, is the height to 
which they will rise above mean still water. For this height Gaillard 
gives the equation 

h h 2 

(7) a = — + C 1 — 

2 1 

in which a is the height of the wave above mean still water, h the total 
wave height, / the wave length, and C is a coefficient, found to be 
about two for a mean depth of twenty-six feet in the Duluth Canal 
and believed to be constant for any particular location. 

59. Energy and Pressure of Waves. — The total energy £ of a wave 
exerted throughout its entire length (in foot pounds) and for one foot 
in breadth is equal to 

h 2 

(8) E = 81h 2 (l — 4.9 — ) 

1* 
The maximum pressure P of a water jet impinging against a square 
foot of area is 

wv- 

(9) P = c 

2g 



1 08 Hydrography. 

in which w equal the weight of a cubic foot of water and c is a co- 
efficient having a maximum value of not exceeding 2. For sea water 
w is approximately 2g and c may be taken as 1.6; hence Equation 9 
becomes 

(10) P = 1.6v 2 

For breaking waves Galliard found that the velocity of the waves was 
increased by the orbital velocity of surface particles so that under these 
conditions the pressure would approximate 

(11) P = 2.3v 2 

Galliard measured with dynamometer pressures as high as 2,370 
pounds per square foot at the end of the Duluth Canal in Lake Su- 
perior. Cunningham gives the maximum pressure of sea waves actu- 
ally recorded by dynamometer as three and one-half tons per square 
foot. 

60. Effects of Waves. — The effect of ocean waves depends upon 
the exposure of the location to extended seaway over which heavy 
windstorms sometimes occur. Professor G. B. Airy shows that in the 
open sea when the depth is great in comparison with the length of 
the wave, the motion of the water at considerable depth below the 
surface decreases in geometrical progression and at depths equal to 
the length of the wave is less than .02% of the surface movement. 
When, however the length of the wave is great in comparison with the 
depth, as in the case of tide waves, the horizontal motion is the same 
from the surface to the bottom. The perceptible agitation sometimes 
extends to depths of almost 100 feet. It is asserted by pilots and mas- 
ters of vessels that in times of storms off Nantucket Shoals the sea 
frequently leaves sand on deck, although the depths are from seventy- 
five to ninety feet. 

The presence of mud in the bottom is a clear indication of the ab- 
sence of wave action, as mud is readily eroded and washed away by 
such action. The absence of mud is not an indication of wave ac- 
tion as conditions may not have been favorable for its formation. In 
various lake harbors in the United States Galliard states that the mud 
bottom of the deeper water changes to sand at the following depths : 

Duluth, Minnesota Lake Superior 55 to 60 feet 

Chicago, Illinois Lake Michigan 40 to 45 feet 

Milwaukee, Wisconsin . . . Lake Michigan 40 to 45 feet 

Cleveland, Ohio Lake Erie : 33 to 38 feet 

Any construction or barrier exposed to the attack of waves must be 
strong enough to resist them and to withstand the energy developed 



Literature. 1 09 

when the wave progress is arrested wholly or in part or its destruc- 
tion will ensue. The force of the waves is the most severe of any 
force of equal intensity to which a structure may be subjected, for as 
Galliard states it is exerted and transmitted in the following ways, viz. : 

First. — By static pressure due to the head of the column of water. 

Second. — By the kinetic effect of the rapidly moving water. 

Third. — By the impact of bodies floating upon the surface and hurled 

by the wave against the structure. 
Fourth. — By the partial vacuum due to the rapid subsidence of the 

wave, producing sudden pressure from within. 

The effects of these shocks may be transmitted through joints or 
cracks, first by hydraulic pressure, second by pneumatic pressure, and 
third by vibrations of the material in the structure. 

In the Wick breakwater, concrete blocks weighing from 80 to 
100 tons and lying from five to ten feet below low water, were swept 
away, while eighty ton blocks lying ten to sixteen feet below low water 
were unmoved. At Coos Bay, Oregon, blocks of stone weighing over 
ten tons have been washed off the jetty above high tide by storm waves. 

LITERATURE 

OCEAN CURRENTS 

Ocean Currents, James Page. Nat. Geog. Mag. April, 1902. 

Origin of Gulf Stream and Circulation of Waters in the Gulf of Mexico, W. 

B. Sweitzer. Trans. Am. Soc. C. C, Vol. 40, 1898, p. 86. Reviews causes, 

course and velocity of current with discussions by others. 
Ocean Currents. Marine Engineering, Jan. 1903. Discussion of Trade 

Winds, Gulf Stream and construction of charts. 
Physical Geography of the Sea, M. F. Maury, Harper & Bros., New York, 1857. 
Geography — Structural, Physical and Comparative, J. W. Gregory. Ten 

pages on causes and effects of currents. Map of location and sources of 

currents. 



Theory of Tides, A. dePreaudeau. Eng. News, Dec. 25, 1886. Explains solar 

and lunar effects on retardation of tides. See also Proc. Inst. C. E., 

Vol. 86, 1885, p. 422. 
Theory of Tides and Prediction of Heights, E. A. Gieseler. Jour. Frank. 

Inst. March and October, 1885. Illustrated mathematical discussion of 

tides. 
Range of Tides in Rivers and Estuaries, E. A. Gieseler. Jour. Frank. Inst. 

Aug. 1891, p. 101. Discussion of ranges on east coast of United States. 
Theoretical Amplitude of Tidal Oscillations, L. DAuria. Jour. Frank Inst., 

Vol. 131, 1891, p. 350. Mathematical discussion. Also Jour. Frank. Inst.,. 

Vol. 123, 1887, p. 331 and p. 409. 



Hydrography. 



Yearly Tides, W. S. Auchencloss. Proc. Engr. Club of Philadelphia, Vol. 9, 
1892, p. 343. 

Tides and Tidal Scour, Joseph Boult. Van Nostrand Mag. Vol. 28, p. 148, 
1883. Observations and statistics on force of tides and tidal currents. 

U. 8. Coast and Geodetic Tide Predicting Machine No. 2, E. G. Fisher. Eng. 
News, July 20, 1911. Description of the latest computing machine for 
predicting tides. 

Effect of Wind and Atmospheric Pressure on Tides, P. L. Ortt. Proc. Inst. 
C. E., Vol. 129, 1897, p. 415. Also Nature, May 27, 1897. 

Limitation of the Present Solution of the Tidal Problem, J. F. Hayford. 
Proc. Inst. C. E., Vol. 138, 1898, p. 535. Also Science, Vol. 8, p. 810. Dis- 
cussions as to methods of study, partly theoretical. 

Atlantic Coast Tides, M. S. W. Jefferson. Nat. Geog. Mag. Dec, 1898. 

Tide Phenomena at Galveston, H. C. Ripley. Trans. Am. Soc. C. E., Vol. 25, 
1891, p. 543. Data and discussions of effect of jetties. 

Tide Indicators, Vidal & Kauffman. Proc. Inst. C. E., Vol. 164, 1905, p. 458. De- 
scription of apparatus. 

Tidal Instruments, Sir Wm. Thomson. Proc. Inst. C. E., Vol. 65, 1880, p. 2. 
Illustrated description of instruments. 

Indicating and Recording the Tides, D. A. Willey. Sci. Am. Apr. 12, 1902. 
Illustrated description of instruments. 

Pacific Coast Tides and Determination of Mean Sea Level, W. P. Dawson. 
Eng. News, June 28, 1916. Discussion of subject on west coast of Can- 
ada. 

Practical Manual of Tides and Waves, W. H. Wheeler, Longmans, Green & Co., 
London, 1906. 

Tidal Researches, Wm. Ferrel, U. S. Coast Survey, Separate publication, 1874. 

Cotidal Lines for the World, R. A. Harris National Geog. Mag. Vol. 17, p. 303, 
1906. 



Force and Action of Waves, J. G. C. Curtis. Proc. Inst. C. E., Vol. 6, 1847, p. 127. 

Discusses proper form of sea walls. 
Force of Waves: Sea Walls near Edinburgh, W. J. M. Rankine. Proc. Inst. 

C. E., Vol. 7, 1848, p. 187. Observations of the effect of wave force. 
Movements of Waves, J. H. Muller. Proc. Inst. C. E., Vol. 21, 1861, p. 470. 

Practical details of works to resist waves. 
Wave Action in Relation to Engineering Structures, Captain D. D. Gaillard. 

Professional Papers No. 31, U. S. Army, 1904. Abstract in Eng. News., 

Vol. 53, p. 189. 
Wave Impact on Engineering Structures, A. H. Gibson. Proc. Inst. C. E. 

Vol. 187, 1912, p. 274. Report of investigation and conclusions. 
The Proper Profile for Resisting Wave Action, Robt. Fletcher. Trans. Am. 

Soc. C. E., Vol. 36, 1896, p. 514. Discussion of different types of sea wall 

profiles. 
Practical Manual of Tides and Waves, Wheeler. Descriptive treatise on 

waves and wave action. Longmans & Green & Co., 1906. 



Literature. 1 1 1 

'Theory of the Water Wave, Morton F. Sanborn. Trans. Am. Soc. C. E., Vol. 

71, 1911, p. 2S4. Conclusions from study of vertical circulation of water. 
Littoral Movements of Neio Jersey Coast with Remarks on Beach Protection 

and Jetty Reaction, Lewis M. Haupt. Trans. Am. Soc. C. E., Vol. 23, 

p. 123, 1890. Discussion of velocity and action of waves. 
Nature of the Tidal Wave, A. Cialdi. Proc. Inst. C. E., Vol. 47, 1902, p. 365. 

General discussion of subject. 
Tidal Waves and the Mascaret, E. S. Gould. Van Nostrands Mag. Sept. 1884. 

Mathematical review of paper in the French, discussing tidal waves, 

bore, etc. 
Ocean Waves and Wave Force, Theo. Cooper Trans. Am. Soc. C. E., Vol. 36, 

1896, p. 139. Discussion of theory and results of investigation. 
A Resume of our Present Knowledge of Wave Motion. Scientific Am. Sup. 

Nov. 19, 1887. 
Memoir an the Experimental Study of Waves, M. L. R. Bertin. Van Nos- 

trand Mag., Vol. 8, 1873, p. 491. Discussion of relation between theory and 

actual results. 
Tidal and Storm Waves, W. H. Wheeler. Engr. London, Apr. 17, 1903. Con- 
siders causes of abnormal solitary waves. 
Progressive and Stationary Waves in Rivers, Vaughn Cornish. Engineering. 

July 26, 1907. Discussion of flood and tidal waves. 
Action of Waves as Affected by the Form of the Bottom, D. A. Stevenson. 

Proc. Inst. C. E., Vol. 46, 1875, pp. 7, 19. Explains increase in wave force 

due to submarine canyon. 
Excavating Power of Waves, South Coast of Ireland, G. H. Kinahan. Proc. 

Inst. C. E., Vol. 58, 1878, p. 281. Discusses transporting effect of waves and 

beach building. 
Magnitude and Telocity of Waves at Sunderland, J. Murray. Proc. Inst. C. 

E., Vol. 8, 1849, p. 200. Observations on height and velocity of waves. 
Telocity of Propagation of Waves, M. Laroche. Proc. Inst. C. E., Vol. 47, 1902, 

p. 363. Brief abstract from L. Academie des Sciences, Vol. 83, p. 74. 
Principles and Practice of Harbor Engineering, Brysson Cunningham, J. B. 

Lippincott Co., Phila., 1908. 



Notes on Geology and Hydrology of the Great Lakes, P. Vedel. Western Soc. 
Civ. Engrs., Vol. 1, 1896, p. 405. Illustrated discussion of climatology, fluc- 
tuations and geology. 

The Temperature of Lakes, Desmond Fitzgerald. Trans. Am. Soc. C. E., 
Vol. 34, 1895, p. 67. Illustrated discussion of lakes, and circulation in 
lakes. 

Lake Currents, W. H. Hearding. Jour. Asso. Eng. Soc. Vol. 11, 1903, p. 363. 
Effect of barometric changes in producing lake level fluctuations. 

Fluctuations of Water Level on Lake Erie. U. S. Weather Bureau, Bulle- 
tin J, 1902. 

Miscroscopy of Drinking Water, G. C. Whipple, Chap. 5, John Wiley & Sons, 
1899. 

Sewage Disposal, Geo. W .Fuller, p. 280, McGraw Hill Book Co., 1912. 



CHAPTER VI 
ATMOSPHERIC MOISTURE AND EVAPORATION 

61. Atmospheric Moisture — Tension and Weight. — The atmos- 
phere always contains moisture or water vapor which unless condensed 
as fog, clouds, etc., is transparent like the other components of the air. 
The maximum amount of vapor which can be contained in a cubic foot 
of space is limited by and increases with the temperature. At any 
given temperature a cubic foot of space or of air will hold only a cer- 
tain maximum amount of moisture, under which conditions it is said to 
be saturated. The weight of moisture contained in a cubic foot of space 
expressed in grains is termed the absolute humidity. The relative hu- 
midity is the percentage of saturation, complete saturation being ioo 
per cent. 

The amount of vapor in a cubic foot of space is independent of the 
presence of air except as the circulation of air accelerates or retards its 
formation. As moisture is received into the atmosphere a portion of 
the air is displaced thereby and the combined weight of air and vapor 
is less than the weight of dry air. A certain amount of vapor in a 
given space will possess a certain tension (or produce a certain pres- 
sure) according to the temperature. The weights of a cubic foot of 
dry air, of a cubic foot of saturated space, of a cubic foot of the air in 
a mixture of air and saturated vapor, and the corresponding weights 
of the mixture, together with the vapor tension and pressure of the air 
in a mixture of air and vapor are shown in Table 5, page 113, and the 
same relations of weights are shown graphically in Fig. 58, page 114. 

Vapor tension is not a measure of the total amount of water vapor 
in the atmosphere overhead, but indicates the amount of water con- 
tained in the air. For complete saturation the relations between the 
weight of moisture in the air (w), in grains per cubic foot, to the 
vapor tension (p) in inches of mercury at any given temperature (t) 
above the freezing point (32 F.) is given by the formula reduced 
from Regnault's experiments by Broch. 1 

11.73 p 

(1) w = 

.9347 + .00204 t 

Below the freezing point vapor tensions do not agree with Regnault's 
experiments but have been determined by Marvin. 2 



1 See Smithsonian Meteorological Tables, p. XXXVII. 

2 See Smithsonian Meteorological Tables, p. XXXVI. 



Atmospheric Moisture. 



113 



TABLE 5. 



Weights of Air, Aqueous Vapor, and Saturated Mixtures of Air and Vapor at 
Different Temperatures, Under the Ordinary Atmospheric Pressure of 
29.921 Inches of Mercury 





Weight 
of cubic ft. 
of Dry Air 
at Differ- 
ent Tem- 
peratures, 
Lbs. 


Elastic 

Force of 

Vapor Inches 

of Mercury 


MIXTURE OF AIR SATURATED WITH VAPOR. 


Tempera- 
ture 


Elastic Force 

of the Air 

in Mixture of 

Air and Vapor 

Inches of 

Mercury 


Weight of Cubic Fool 
Mixture op Air and 


OF THE 

Vapor 


Degrees 
Fahr. 


Weight 

of the Air. 

Lbs. 


Weight of 

the Vapor, 

Lbs. 


Total 

Weight of 

Mixture 

Lbs. 





.0864 


.044 


29.877 


.0863 


.000079 


.086379 


12 


.0842 


.074 


29.849 


.0840 


.000130 


.084130 


22 


.0824 


.118 


29.803 


.0821 


.000202 


.082302 


32 


.0807 


.181 


29.740 


.0802 


.000304 


.080504 


42 


.0791 


.267 


29.654 


.0784 


.000440 


. 078840 


52 


.0776 


.388 


29.533 


.0766 


.000627 


.077227 


62 


.0761 


.556 


29.365 


.0747 


.000881 


.075581 


72 


.0747 


• 785 


29.136 


.0727 


.001221 


. 073921 


82 


.0733 


1.092 


28.829 


.0706 


.001667 


.072267 


92 


.0720 


1.501 


28.420 


.0684 


.002250 


.070717 


102 


.0707 


2.036 


27.885 


.0659 


.002997 


.068897 


112 


.0694 


2.731 


27.190 


.0681 


.003946 


.067046 


122 


.0682 


3.621 


26.300 


.0599 


.005142 


.065042 


132 


.0671 


4.752 


25.169 


.0564 


.006639 


.063039 


142 


.0660 


6.165 


23.756 


.0524 


. 008733 


.060873 


152 


.0649 


7.930 


21.991 


.0477 


.010716 


.058416 


162 


.0638 


10.099 


19.822 


.0423 


.013415 


.055715 


172 


.0628 


' 12.758 


17 . 163 


.0360 


.016682 


.052682 


182 


.0618 


15.960 


13.961 


.0288 


.020536 


.049336 


192 


.0609 


19.828 


10.093 


.0205 


.025142 


.045642 


202 


.0600 


24.450 


5.471 


.0109 


.030545 


.041445 


212 


.0591 


29.921 


0.000 


.0000 


.036820 


.036820 



The ratio — is practically constant for small ranges of temperature 

but varies for temperatures from -20 c to ioo° F. as shown graphically 
in Fig. 59, 3 page 115. 

The relations of absolute and relative humidity to the temperature 
and weight of moisture in the air are given in Fig. 60. From this dia- 
gram the relation of absolute moisture to absolute or relative humidity 
at various temperatures can be determined. For example : if air at 
ioo 01 F. contains six grains of vapor, it is practically thirty per cent, 
saturated. If the temperature of the air falls to 72 F., the percent- 
age of saturation will reach approximately seventy per cent, and if the 



3 The ratios of weight to vapor tension (Fig. 59) and the weights of sat- 
urated vapor per cubic foot of air (Fig. 60) are calculated by Formula 1 for 
temperatures above 32° F. and are taken from the tables of the Weather 
Bureau (Psychrometric Tables, Table XII, p. 83, by C. F. Marvin. U. S. 
Weather Bureau W. B. No. 225) for ratios below 32° F. 
Hydrology — 8 



114 



Atmospheric Moisture and Evaporation. 



temperature falls to 62 °' F. the air will be over saturated, the dew point 
will be passed and condensation will begin. When air is partially sat- 
urated and its temperature is reduced, the percentage of saturation 
will increase, and when the saturation reaches 100 per cent, the invis- 
ible vapor will begin to condense into visible moisture. Under these 
conditions the corresponding temperature is called the dew point. 


















02 


Pounds /oer Cubic Fbor. 
04 






06 












OS 




































































200 










































\ 






























































\ 


































nC 






























\ 
































■p) 
































\ 






























$ 




































\ 


























































^ 






\ 
























£ 








































\ 


1 
















\ 




t 


0/ 




































^ 


\ 
















§ 

1 

1 




$ 










































\ 


















7 










































Si\ 




















/ 












































<&A 


v \o 














1 
















































■> 












1 


/ 


















































S^C 










* 
































































1 

K 50 






























































































































































































































































































































































































































































/OO 



300 400 

Grains per Cubic Foot. 



500 



600 



Fig. 58. — Weight of Air and Saturated Aqueous Vapor at Normal Sea Level 
Pressure for Various Temperatures (see page 112). 

The dew point may therefore be defined as the temperature of the at- 
mosphere at which, with the amount of vapor it contains, it will be- 
come saturated. 

62. Atmospheric Temperatures and Moisture at High Alti- 
tudes. — In general the temperature of the atmosphere at all seasons 
of the year decreases with the altitude (see Sec. 32), except at moder- 
ate elevations (below 10,000 feet) where atmospheric disturbances 
sometimes cause a temporary reversal of this condition (see Fig. 61, 
page 116). Fig. 62/ page 117, illustrates the temperature gradients as 
they commonly exist during summer (Curves 1 to 4 inclusive) and 
winter (Curves 5 and 6). The straight line numbered 8 shows the 



* See Bulletin Mt. "Weather Observatory, Vol. II, part 1, 1909, p. 4. 



Temperatures and Moisture. 



115 



adiabatic gradient for dry air and line 7 shows the temperature gradient 
for saturated air, starting with an assumed summer sea level tempera- 
ture of 68° F., while lines 9 and 10 indicate the same gradients for 



Fig. 59.- 



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Fig. 60. — Weight of Aqueous Vapor at Various Temperatures and Degrees of 
Saturation (see page 113). 

winter conditions with an initial sea level temperature of 48 F. 
Lines 7 and 9 therefore represent the theoretical temperatures which 
would be attained by rising currents of moist air during the summer 
and winter respectively, and it is important to note how closely the ac- 
tual observed data correspond with the theoretical condition. The 
lines 8 and 10, showing the theoretical adiabatic gradient for dry air 
show the temperature gradient which would be approximated by de- 



16 



Atmospheric Moisture and Evaporation. 



scending currents of air from which the moisture has been partially 
removed by the low temperatures of the higher altitudes. 

It should here be noted that if the air from an altitude of 30,000 
feet were to descend to the sea level without radiation, the tempera- 
ture would be raised by compression to about 136 F. in summer and 
to 82 F. in winter, on the basis of these adiabatic gradients. The 
radiation is so great, however, that the descending currents from 

December 2/ December 22 

PM. A.M. 

12 J 2 3 4 5 6 7 8 9 10 II 12 I 2 3 4 5 6 7 6 9 1 II 12 I 2 3 




Fig. 61. — Free Air Temperatures in Degrees Fahrenheit above Drexel, Ne- 
braska 5 (see page 114). 

higher altitudes are usually much lower than air temperatures at the 
surface, as is evident whenever a high barometric condition prevails. 

As might reasonably be expected, the mean annual temperature for 
any locality will decrease with the altitude and in approximate propor- 
tion to the temperature gradient for saturated air. Fig. 63 shows the 
theoretical temperature gradients for saturated air from a summer 
sea level temperature of 68° (A) and a winter sea level temperature 
of 48 (B), also the mean annual temperature gradients for closely 
adjoining stations in Colorado, California, New England and the Euro- 
pean Alps, and the approximate agreement of the actual temperature 
gradients of the mean annual temperatures with the theoretical tem- 
perature gradients is shown. 

From Sec. 59 it is evident that on account of the lower temperature 
of the higher altitudes, the vapor tensions and the consequent vapor 
content of the air must decrease rapidly with the altitude. That the 

s Monthly Weather Rev. Sup. No. 3, 1916, p. 36. 



Temperatures and Moisture. 



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Fig. 62. — Vertical Temperature Gradients in Free Air (see page 114). 



Atmospheric Moisture and Evaporation. 



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Fig. 63. — Theoretical Temperature Gradient and Decrease in Mean Annual 
Temperature with Altitude (see page 116). 



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Fig. 64.— Vertical Distribution of Water Vapor on Clear Days (see page 119). 



Distribution of Atmospheric Moisture. 



9 



facts agree with the theory is made evident by Fig. 64, 6 where the 
actual vertical distribution of vapor for various seasons of the year is 
shown. 

The quantity of vapor in the atmosphere decreases with the increase 
in altitude more rapidly than the pressure decreases, as will be 
seen by reference to Fig. 65, in which the decrease in vapor tension and 

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Percent of ToM Pressure of>5eoL.eve/. 

Fig. 65. — Decrease of Vapor Tension and Pressure with Increase in Altitude. 

in atmospheric pressure is given in percentages of such tension and 
pressure at sea level. 7 

Vapor tension is practically proportional to quantity of vapor, hence 
the diagram shows the relative vapor content of the atmosphere at dif- 
ferent elevations. About one-half the total moisture is contained in 
the atmosphere below an elevation of 6,500 feet, about three-quarters 
below 13,000 feet, and about nine-tenths below 21,000 feet. Hence on 
a clear day in winter with an absolute humidity of one grain per cubic 
foot at the surface of the earth, the total moisture in the atmosphere 
distributed over the surface of the earth would equal about .25 inches ;. 
while in summer with six grains of moisture per cubic foot at the sur- 



e See Bulletin Mt. Weather Observatory, Vol. 4, part 3, 1911, p. 128. 
7 See Handbook of Climatology by Dr. Julius Hann. Translated by Prof. 
R. De C. Ward, 1903, p. 286. 



i 20 Atmospheric Moisture and Evaporation. 




Fig. 66. — Average Distribution of Atmospheric Moisture in the United States 
for January. (Grains of water per cubic foot of air) (see page 121). 




Fig. 67. — Average Distribution of Atmospheric Moisture in the United States 
for July. (Grains of water per cubic foot of air) (see page 121). 



Distribution of Atmospheric Moisture. 



21 



face, the total atmospheric moisture if so distributed would equal about 
1.5 inches. 

63. Geographical Distribution of Normal Atmospheric Mois- 
ture. — The moisture of the atmosphere is the result of vaporization 
from water surfaces, from vegetation and from other moist surfaces 
and is therefore usually found in greater absolute and relative quanti- 
ties near the sources from which the moisture may be derived. On 




Fig. 68. — Average Annual Relative Humidity in the United States (percent- 
age). 

the ocean in the Doldrums the air is always near saturation. This is 
due to the Trade Winds which, flowing over the warm surfaces of the 
ocean with slowly rising temperatures as they advance, are continually 
supplied with vapor and maintained in an almost saturated condition. 
Over the deserts where the supply of moisture is very small the quan- 
tity of vapor in the atmosphere is far below its capacity. In general, 
the amount of moisture decreases toward the center of a continent, but 
this is modified by normal rainfall conditions, by the presence of large 
lakes, extensive forests and swamps and by prevailing wind move- 
ments. 

The average distribution of atmospheric moisture in the United 
States in January and July is shown in Figs. 66 and 6j respectively, 
page 120, and the average annual relative humidity in the United 
States in terms of percentage of saturation is shown by Fig. 68. 



22 



Atmospheric Moisture and Evaporation. 



64. Variation in Absolute and Relative Humidity. — Absolute hu- 
midity will vary at every locality from hour to hour and from day to 
day with atmospheric temperature, pressure, wind movement and re- 
sulting evaporation. Relative humidity will vary to a still greater ex- 















































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M6/E6M6/£6/>76/£6/*76/a6M6/2 6M 
Aug.2. Aog.3. Aug 4. Aug 5 Aug 6. 

Fig. 69. — Relative Humidity, Temperature, Absolute Humidity and Rainfall 

from Midnight, August 1 to Midnight, August 6, 1916, at Madison, Wis.* 

tent, as with the same moisture content the degree of saturation will 
vary with the hourly variations in temperature. Both absolute and 
relative humidity will vary in still greater degree in different localities. 
The variation in temperature and both relative and absolute humidity 
from hour to hour at Madison, Wisconsin, for the period August i to 
6, 1916, are shown in Fig. 69, page 122. The amount of precipitation 
during this period and the consequent changes in atmospheric mois- 
ture during this period are of interest. The variation in absolute hu- 
midity from month to month at various typical stations in the United 
States is shown in Figs. 70 and 71, page 123. 



Compiled from data furnished by E. R. Miller. U. S. W. B. 



Sources of Atmospheric Moisture. 



123 



65. Interchange of Moisture Between Air and Land or Water 

Surface. — The moisture of the atmosphere is furnished by evaporation 
from water surfaces which cover nearly three-fourths of the earth's 
surface. The oceans, lakes, swamps and river surfaces, therefore, 
furnish the largest portion of atmospheric moisture. Additional 
sources are the ground surface, which is usually somewhat moist, and 
the transpiration of plants and animals. Vegetation through its roots, 
which often penetrate the soil to considerable depths, draws from 
the ground storage moisture which would otherwise remain as ground 
water. It is apparent that the wind will carry some of the vapor from 



i 8 



•3 O 

^t Jan Feb Mar. Apr. Mai/ Jun Jul fluq Sept. Oct Nov Dec 

Fig. 70. — Variations in Average Ab- 
solute Humidity at Various Sta- 
tions (see page 122). 

















































































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Fig. 71. — Variation in Average Ab- 
solute Humidity at Various Sta- 
tions (see page 122). 

























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the continent to the sea and some of the vapor from the ocean to the 
adjacent continents. Bruckner s has estimated that the net results of 
this interchange of vapor between the oceans and land is that only 
seven per cent, of the precipitation of the land comes from moisture 
received directly from the sea. The author believes, however, that 
this estimate is too small. The moisture of the air over continental 
areas is most largely drawn from the inter-continental water surfaces 
of lakes, swamps, marshes and streams, from moist earth areas and 
from the transpiration of forests and other vegetation and probably 
does not receive more than from twenty-five per cent, to thirty-five per 
cent, from the oceans. (See Table 13, page 165.) 

Evaporation is continually taking place from a moist surface when- 
ever the water is above the dew point temperature of the air which 
is in contact with it. Whenever the water or other surface in contact 
with moist atmosphere falls in temperature so that the air in contact 
is reduced in temperature below the dew point, condensation occurs 



s The Relation of Forests in the Atlantic Plain to the Humidity of the Cen- 
tral States end Prairie Regions, by Dr. Raphael Zon. Science, Vol. 38, p, 69. 



24 



Atmospheric Moisture and Evaporation. 



and dew is formed on the exposed surface. There is therefore a con- 
stant exchange of moisture between the air and moist surface, some- 
times by evaporation from the water to vapor and sometimes by con- 
densation from vapor to moisture. The observed evaporation from 
water surfaces is the net result of this interchange of moisture. 

66. Heat Changes Involved in Evaporation and Condensation. — 
As water increases in temperature it must absorb heat, as in the case 



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Fig. 72. — Relations of Heat Energy in Water.* 

of all other bodies. When however water changes its physical form 
from solid (ice) to liquid (water) or from liquid to vapor, a large 
amount of heat is absorbed and becomes latent. The heat necessary 
for the increase in temperature through a wide range is shown by 
Fig. 72, page 124. In this diagram the amount of heat required to 
raise the temperature of water is compared with the amount of heat 
necessary to raise the temperature and to melt gold and steel. The 
latent heat of melted ice and of vaporized water, which is not manifest 
by an increase in temperature, is shown by the horizontal lines of the 
diagram. 

From this diagram it becomes evident that when water is evapo- 
rated, a considerable amount of energy must be absorbed from some 
source. This energy may be obtained by the reduction of temperature 
in the water itself or of the body in which it is contained or by radiant 
energy from the sun or from adjacent bodies. In the same manner 



Lecture by G. H. Babcock. Sci. Am. Sup. Dec, 1887. 



Heat Changes in Evaporation and Condensation. 1 25 

condensation is accompanied by a transformation of latent to percep- 
tible heat which is delivered to the atmosphere and has an important 
effect on the dynamics of storms. 

Dew and frost are caused by the radiation of heat from the earth's 
surface into a clear atmosphere, the reduction in the temperature of 
the adjoining air below the dew point, and consequent condensation. 
Low foe"s are the result of a similar radiation and reduction of tern- 




Fig. 73 — Relative Annual Evaporation from Free Water Surfaces in the 

United States. 

perature in the lower atmosphere. High fogs and clouds are the result 
of dynamic cooling due to expansion of rising vapors. The condensed 
particles of moisture which make up clouds and fogs are very small, 
varying from .ooi to .00025 inch in diameter, and they are maintained 
in suspension in the atmosphere by ascending air currents. As a drop 
of water .001 inch in diameter would fall at the rate of less than two 
inches, per second, 9 it requires a feeble upward current to maintain it 
in suspension. 

67. Evaporation. — Evaporation takes place from moist surfaces and 
from the water surfaces whenever such surfaces are in contact with 
unsaturated air. Fig. 73, is a map showing roughly the annual 
evaporation which takes place from water surfaces at various points 
within the United States. This map and the table of monthly 



9 See Meteorology, by W. I. Milham, 1912, p. 232. 



1 26 Atmospheric Moisture and Evaporation. 

evaporation in the Appendix are taken from data given in the Monthly 
Weather Review of September, 1888. The Weather Review observa- 
tions were deduced from readings of dry and wet bulb thermometers 
as observed at various signal Service Stations in 1887 and 1888. 
These deductions were supplemented by observations at several sta- 
tions by means of the Piche evaporimeter. This map (Fig. 73) shows 
the annual evaporation rates in the greater portion of the United 
States to be equal to or greater than the local annual rainfall. The total 
annual evaporation as shown by the map is, however, based on free water 
surfaces only, and evaporation from ground surfaces .takes place only 
from occasional moist surfaces which exist after rains. 

While evaporation, like rainfall and other meteorological phenomena, 
varies from year to year in accordance with the variation in the con- 
trolling factors, yet this variation is apparently much less than the 
variation in most other meteorological phenomena such as rainfall, 
temperature, etc. This map and the table therefore indicate relative 
conditions at the various stations and roughly the evaporation from 
free water surfaces. The comparative monthly evaporations at sixteen 
stations distributed throughout the United States, and based on these 
tables, are shown graphically by Fig. 74. At a number of places in the 
United States evaporation observations have been made for a number 
of years and from the data thus collected a general knowledge of local 
variations that occur in evaporation can be obtained. 10 When the 
amount of evaporation becomes an important element in engineering 
problems, a study must be made in detail of the local conditions which 
modify its distribution and total amount. 

68. Factors of Evaporation. — Evaporation at any time or place 
will depend on various physical and meteorological conditions most of 
which will vary from time to time. The meteorological conditions 
frequently vary with considerable rapidity from hour to hour (see Figs. 
21, 32 and 69). The principal meteorological factors are: vapor ten- 
sion, temperature and wind movements in which the variations are con- 
siderable and cannot be forecast with any degree of certainty, except as 
to monthly average which can be foretold only within certain rather 
definite limits. In consequence these factors must be considered 
broadly for practical purposes. 

The physical factors to be considered are : altitude and nature of the 
surface from which evaporation occurs, and the subsurface so far as 
it affects the amount of evaporation. In general, the surface condi- 
tions may broadly be divided into land and water surfaces. 



10 See Literature at end of chapter. 



Factors of Evaporation. 



27 



Dec Jan 



DecJan 



Dec Jan 



Dec 




North Atiantic 
New Haven Connecticut 



South At /ant, 
Austista. Ga 



St Lawrence Onto ffiver 

Detroit. Mich Cincinnati. Ohio 



Jan 



Dec Jan 



Dec Jan 



Dec Jan 



Dec 




Missouri Driver 
Topeka. h(an Heiena. Mont 



F?ed Ffiver 
Mooreheaa'. Minn 



North facific 
Oiympia. Wash 



Jan 



Dec Jan 



Dec Jan 



Dec Jan 



Dec 




Co/umbia /-fiver South D^acific Co/oraaio Driver Great Gas/'n 

3/Dokane. Wash Dacramenfo. Ca/ Yuma. Ariz. Winnemucca. Nev 

Fig. 74. — Monthly Evaporation from Free Water Surface at Sixteen Stations 
in the United States (see page 126). 



1 28 Atmospheric Moisture and Evaporation. 

The body of water from which evaporation takes place may be small 
or large, exposed or protected from the wind, it may be shallow or deep, 
it may be free or filled with more or less vegetation. If exposed to 
wind movements, if small, shallow or filled with vegetable growth, evap- 
oration will be increased. In the summer when evaporation is at a 
maximum more water will evaporate from small and shallow bodies than 
from deep and large bodies on account of the increased temperature in 
the small bodies of water. The presence of vegetation will also add to 
the amount of water loss as evaporation will be augmented by the trans- 
piration of the growing plants. Evaporation from ice surfaces while 
comparatively small is still a factor not to be ignored. 

The evaporation from land surface normally depends upon the 
amount, intensity and distribution of the rainfall and also on the moisture 
conditions of the surface. Light rains may be evaporated from the 
surface while much of a heavy rainfall will percolate into porous soil 
beyond the reach of evaporating influences. Land surfaces may be 
saturated, moist, dry, frozen or covered with snow or ice. They may 
be of loam, sand, clay or rock of varying characters and underlaid with 
various materials in endless varieties and of varying porosities. The 
surface may also be bare or cultivated ; it may be covered with crops of 
various characters ; it may be grass land or forests. The exposure to 
winds is also important. 

It is evident that comparatively more evaporation will take place from 
wet than from dry land and that in the latter case no evaporation will 
take place unless the capillarity of the soil or the roots of plants draw 
the water from lower levels. 

It is apparent therefore that the whole question of evaporation from 
any drainage area is a very complicated subject that can be ascertained 
with no great degree of accuracy but which nevertheless must be in- 
vestigated and understood so far as practicable in order that many im- 
portant problems of hydraulic engineering may be solved with as great 
a degree of certainty as the conditions permit. 

69. Vapor Tension. — The rate of evaporation at any time depends 
not on the relative humidity which varies rapidly with atmospheric 
temperature, but on the vapor tension due to the temperature of the 
water surface (V) and the vapor tension in the layer of air in contact 
with the water surface (v). If this difference be large, evaporation 
will be rapid, while evaporation will decrease with the difference and 
will change to condensation when this difference is negative (see 
Fig. 75, page 129). 



Vapor Tension. 



129 



Just how these vapor tensions should enter into a correct formula 
for evaporation has not yet been accurately determined, although a 
number of such formulas have been proposed. The experiments of 



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06 .08 JO ./£ M 

Evaporar/or? joer- /-/oar //7c, h e5 

-Effect of Vapor Tension on Evaporation 



/8 



SO 



Mr. Desmond Fitzgerald, made in the city of Boston show that evapo- 
ration (e) varies in accordance with formula (2). 11 
(2) e = .014 (V — v) + .0012 (V — v) = 

This formula was determined from experiments platted in Fig- 
ure 75. Other experiments seem to indicate, however, that the for- 
mula is not of general application even when corrected for wind, alti- 
tude, etc. 12 



n See Evaporation, by Desmond Fitzgerald. Trans. Am. Soc. C. E., Vol. 15, 
p. 581 et seq; also studies of evaporation, by Prof. F. H. Bigelow, U. S. Weather 
Review, Vol. 35, p. 311 (in which various formulas are compared). 

12 See Studies of the Phenomena of the Evaporation of Water over Lakes and 
Reservoirs, by Prof. F. W. Bigelow. Monthly Weather Review, July 1907, 
p. 311. 

Hydrology — 9 



30 



Atmospheric Moisture and Evaporation. 



70. Temperatures. — These vapor tensions depend on the tempera- 
tures of the water and the dew point temperature of the air, both of 
which vary continually and therefore cannot be of general value (even 
were their relations definitely established) for estimating monthly or 
annual evaporation in which the engineer is more directly interested, 
although they may prove important as a means for detailed investiga- 
tions. 

Some of the comparative variations in air, water and earth tempera- 
tures have already been shown in Fig. 14, page 48. Similar tempera- 




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August 24, 1905, at Arlington Heights. 

ture variations relative to exposure in sun and shade and between 
moist and dry soils are shown in Fig. y6. lz 

The waters of lakes, reservoirs and canals, in which the determina- 
tion of the amount of evaporation becomes of importance to the en- 
gineer, are in general exposed to the sun and weather, and while their 
temperatures do not vary hourly and daily directly with the tempera- 
ture of the air, there is a more direct relation between the average 
monthly temperature of air and water in any locality. 

The investigations of Dr. Fortier 14 do not indicate any constant re- 

13 Bulletin 177 U. S. Dept. Agriculture, Evaporation Losses in Irrigation, by 
Dr. Samuel Fortier, p. 42, Fig. 17. 

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Pig. 77. — Relation of Evaporation to Temperature at Various Stations (see 

page 132). 



1 32 Atmospheric Moisture and Evaporation. 

lation between temperature and evaporation, although in general in- 
creased temperature results in increased evaporation. (See Fig. jj y 
page 131). 

Fig. 77 and some of the following diagrams seem to indicate that 
no evaporation would take place below certain temperatures, which 
vary more or less in each particular case. This indication is undoubt- 
edly erroneous as evaporation will occur even from the surface of snow 
and ice with other conditions favorable, hence these lines cannot be 
straight as the diagrams in general indicate. 

Mean atmospheric temperatures are the data most widely available, 
and it is important that such data be utilized if possible as one of the 
factors for the practical estimation of evaporation. That there is a 
fairly close relation between mean monthly temperatures and mean 
monthly evaporations for any given locality has been demonstrated by 
many evaporation experiments. The experiments by Fitzgerald dem- 
onstrate such a relation. (See Fig. 78, page 134.) General average 
relations determined by various experiments are shown in Fig. 79, 15 
page 135, from which it will be seen that while such a relation seems 
to be fairly constant for any given locality, other factors so modify 
the results that the relation cannot be applied in any general way with- 
out at least taking into account other modifying factors. Such factors 
from previous consideration must evidently include at least altitude 
and wind velocity. 

71. Wind Movements. — Evaporation is greatly promoted by atmos- 
pheric currents which have perhaps the most marked effect of any sin- 
gle influence. A brisk wind will rapidly remove the air which is in 
contact with the water or moist surface and more or less nearly sat- 
urated, and substitute dry air or air which is of lower humidity. 
The vapor which results from evaporation will, in the absence of wind, 
hang like a blanket over the water surface, and by reducing the dif- 
ference in vapor tension (V — v), materially reduce evaporation. A 
slight breeze will quickly remove the vapor blanket over an evapora- 
tion pan, thus greatly facilitating evaporation ; while in large lakes and 
reservoirs the evaporation will be hastened on the windward side but 
will decrease on the other side, thus effectively reducing the evapora- 
tion of the larger body of water below that indicated by the evapora- 
tion pan. 



is A study of the Depth of Annual Evaporation from Lake Conchos, Mexico, 
by Edwin Duryea and H. L. Haehl. Trans. Am. Soc. C. E., Vol. 80, 1916, p. 1829 
et seq. See also Evaporation, by Desmond Fitzgerald. 



Wind Movement. 1 33 

Dr. Fortier 16 found that the daily evaporation from pans increased 
from .07 to .85, or an average of forty-six per cent, per mile of wind 
movement, while Fitzgerald found the increase to be 1 -f- .013, and 
Carpenter 17 found the increase to be 1 -\- .0015W, in which w = wind 
movement in miles per hour. As in general the velocity of the wind 
increases with altitude, this may account for the very rapid increase 
in evaporation with altitude and temperature, shown in Fig. 81. Wind 
movements as recorded at Weather Bureau Stations are of little value 
for the determination of evaporation from water surfaces, as the point 
of observation is usually at a considerable elevation and the records 
give little information as to the actual air movement closely adjoining 
the water surface. Fitzgerald found that at Boston the air movement 
at the surfaces was about one-third of the movement recorded on a 30 
foot tower. 

The velocity of the wind decreases rapidly as the surface of the 
earth is approached. Biglow found at Indio by placing one ane- 
mometer 10 feet above the evaporation pan and another anemome- 
ter at the elevation of the pan, that usually the lower anemometer re- 
corded from 30 to 50 per cent, less wind movement than the upper 
one. He therefore concluded that "every pan must invariably be sup- 
plied with its own anemometer whenever evaporation observations are 
made on land or on large bodies of water." He also concludes that 
wind effects equal 1 -\- .043W. 18 This is three and one-half times that 
used by Fitzgerald and thirty times that used by Carpenter. 

72. Effect of Altitude on Factors of Evaporation. — A reduction in 
atmospheric pressure increases evaporation when wind movements, tem- 
perature and relative humidity remain the same. On this account, other 
things being equal, evaporation is greater in the mountains than in the 
lowlands. This is shown by the fact that the temperatures of vaporiza- 
tion (the boiling point) is greatly reduced at increased altitudes. This 
critical temperature is reduced 19 F. between sea level and an altitude 
of 10,000 feet. The reduction in boiling point due to altitude is shown 
in detail in Table 6. Temperature, however, which so greatly affects 
evaporation, decreases so much more rapidly than pressure that the 
actual evaporation at high altitudes is in general less than on the low 
lands in the immediate vicinity (see Fig. 80, page 136). 

Duryea and Haehl have apparently determined fairly constant re- 



16 See Bulletin 177, U. S. Dept. of Agriculture, p. 45. 
i" Weather Review, July, 1907. 
is Weather Review, Feb. 1910. 



1 34 Atmospheric Moisture and Evaporation. 

TABLE 6. 
Boiling-Point of Water Corresponding to Barometric Pressure and Altitude 

Above the Sea-Level. 



Boiling-point 


Barometer 


Alti- 
tude 
Feet 


Boiling-point 


Barometer 


Alti- 
tude 
Feet 


F° 


C° 


Inches 


mm. 


F° 


0- 


Inches 


mm. 


184 


84.4 


16.79 


426.5 


15221 


200 


93.3 


23.59 


599.2 


6304 


185 


85.0 


17.16 


43H.0 


14649 


201 


93.8 


24.08 


611.6 


5764 


186 


85.5 


17.54 


445.5 


14071 


202 


94.0 


24.58 


624.3 


5225 


187 


86.1 


17.92 


455.4 


13498 


203 


95.0 


25.08 


637.0 


4697 


188 


86.6 


18. 32 


465.3 


12934 


204 


95.5 


25.59 


650.0 


4169 


189 


87.2 


18.72 


475.6 


12367 


205 


96.1 


26.11 


663.2 


3642 


190 


87.7 


79.13 


486.0 


11799 


206 


96.6 


26.64 


676.7 


3115 


191 


88.3 


19.54 


496.3 


11243 


207 


97.2 


27.18 


690.4 


2589 


192 


88.8 


19.96 


507.0 


10685 


208 


97.7 


27.73 


704.3 


2063 


193 


89.4 


20.39 


517.9 


10127 


209 


98.3 


28.21) 


718.6 


1539 


194 


90.0 


20.82 


528.8 


9579 


210 


98.8 


28.85 


752.8 


1025 


195 


90.5 


21.27 


540.0 


9031 


211 


99.4 


29.42 


747.3 


512 


196 


91.1 


21.71 


551.3 


8481 


211 


100.0 


30.0 


762.0 


sea 


197 


91.6 


22.17 


563.4 


7932 


below 


sea 


level 




level 


198 


92.2 


22.64 


575.0 


73s 1 


213 


100.5 


30.59 


777.0 


512 


199 


92.7 


23.11 


587.0 


6841 













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Fig. 78. — Relation of Evaporation and Temperature at Boston, Mass. (see 

page 132). 

lations for altitude, temperature and evaporation among certain 
stations in the southwest portion of the United States. From these 
investigations Fig. 8i, 19 page 136, has been made. The data used by 
Duryea and Haehl are more or less indefinite and imperfect. This is 
especially true of the. data for Carlsbad which are averages of two 
stations, the data from both of which are believed to be in error. 
Their conclusions are intended to apply only to the region of the Great 
Plateau from Mexico north to Colorado and Utah. 



19 Evaporation from Lake Conchos, Duryea and Haehl. 



Effect of Altitude. 



135 



While the relations shown in Fig. 81, between the stations at Albu- 
querque, Elephant Butte, Carlsbad and Austin seem fairly consistent, 
similar data shown on this diagram for El Paso, which is in the same 
district, are discordant and it would seem that the relations indicated 
are more a matter of chance than of law. Similar data for Boston, 
Mass., Columbus, Ohio and Menasha, Wisconsin are still more dis- 
cordant and indicate that even if this diagram fairly represents a local 
relation, it cannot be regarded as general. 

In general it is held that with temperature, wind movements and 
relative humidity equal, evaporation will be inversely proportional to 

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Fig. 79. — Relations between Mean Evaporation and Temperature at Various 
Stations (see page 132). 



atmospheric pressure ; hence at a given temperature evaporation should 
increase directly with the reduction in barometric pressure, due to al- 
titude. 

In Fig. 82, page 137, the theoretical evaporation at various eleva- 
tions is shown relative to sea level under similar conditions of (mean 
monthly) temperature, wind and humidity, in accordance with the 
above law. On this diagram is platted the increase in evaporation 
with altitude and constant temperature of the station previously con- 
sidered in Fig. 81. The discordant results indicate that the wind 
movements or relative humidity at the higher altitudes have had a de- 
cided accelerating effect on evaporation. 

73. Evaporation of Snow and Ice. — Snow and ice exposed to at- 
mospheric agencies decrease in volume by sublimation due to the same 



136 



Atmospheric Moisture and Evaporation. 



SI 



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Depth of Weekly Evaporation -Inches 



Fig. 80. — Influence of Altitude on Evaporation on Eastern Slope of Mount 
Whitney, Cal. (see page 133). 



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Fig. 81. — Relations between Evaporation and Temperature at Various Alti- 
tudes (see page 134). 

factors which cause evaporation from moist land and water surfaces. 
With the thermometer below the freezing temperature, the wind is ap- 
parently the greatest factor in this phenomena. The information on 
this subject is fragmentary and the loss difficult to determine on account 



Evaporation of Snow and Ice. 



37 



of varying conditions even within limited areas. Fitzgerald 20 found 
that average evaporation from snow was 6 inches per month and con- 
cluded that evaporation from ice is nearly twice as rapid as from snow, 
and might equal six inches per month with a 12-mile wind. Lee 20 es- 
timated the loss from snow field on the highest mountain areas (the 
Sierra Nevadas) at y.y inches (of water) per season. Lippincott' 1 
estimated the season's loss on the high mountains of the San Bernardino 
Valley at 14 inches of water. Baker' 2 made various experiments at 



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Depth of Month 1 1/ Fi/aporaf/o.i in Inches 

Fig. 82. — Relations between Evaporation and Pressure (see page 135). 

the Utah Experimental Station which are shown relative to the simul- 
taneous temperature in Fig. 83, page 138 on which are also plotted 
Lippincott's observations, all reduced to monthly rates of evaporation. 
The wide departure from a curve drawn through the centers of gravity 
of the various groups of ten points shows the influences of wind, vapor 
tension, etc. 

The effect of forests in decreasing sublimation seems largely to be 



20 Evaporation, by Desmond Fitzgerald. Trans. Am. Soc. C. E., Vol. 15, 
p. G10. Water Resources of a part of Owens Valley, Cal., by Chas. L. Lee, 
Water Supply Paper No. 294, p. 50. 

1 Water Supply of San Bernardino Valley, by J. B. Lippincott, Nineteenth- 
Annual Rept. U. S. G. S. Part 4, p. 624. 

: - Some Field Experiments on Evaporation from Snow Surfaces, by F. S. 
Baker. Mon. Weath. Rev. July, 1917, p. 363. 



138 



Atmospheric Moisture and Evaporation. 



due to their influence in checking wind velocity, thus affecting drifting 
and erosion, and in shading thus diminishing the direct insolation. On 
the other hand these effects may be offset, particularly in the case of 
coniferous forests, by the lodgment of snow on the trees themselves 



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Evaporation from Snoyv-fncnes per Monfh. 

Fig. 83. — Observations of Evaporation from Snow. 

which increases the area exposed to evaporative action. This subject 
becomes of special importance in connection with the study of the rela- 
tion of mountain snowfall to water supply for cities, irrigation and 
water power. 

74. Evaporation From Land. — The character and depth of the 
soil or other surface material, the condition of the surface, whether 
bare, cultivated or with vegetation, its composition and underdrain- 
age as well as the various factors hitherto discussed, all have import- 
ant influences on the amount of evaporation from the land. 



Evaporation From Soil 



139 



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Fig. 85. — Relations between Rainfall and Evaporation (see page 141). 



Evaporation from Land. 141 

The various experiments on soil evaporation made in the past are 
all subject to various experimental errors but these errors are much 
less in magnitude than the differences that will occur with various 
conditions of soil, so that they may all be regarded as fairly illustra- 
tive of the various divergences which will be found to exist in differ- 
ent locations often on the same drainage area. In all of these exper- 
iments the annual rainfall was measured and compared with the 
amount of water which percolates through the soil. The difference 
between these two quantities was estimated as soil evaporation. 
In some cases different soils were compared with each other and 
with the water evaporating from free water surfaces, and in one 
case also from a shaded water surface. The average results of each 
series of experiments are shown in Table 7. Fig. 84, page 139, shows 
the relative rainfall and evaporation as determined from experi- 
ments : (A) by Dickinson and Evans at Hertsfordshire, England 
( 1835-1875) ; (B) by Charles Greaves at Lee Bridge, England (1860- 
l &75) '> (C) by Gilbert and Lawes at Rothamsted, England (1871- 
1890) ; and (D) by the Geneva (N. Y.) Experimental Station (1883- 
1887). In these diagrams should be noted the differences in evapor- 
ation between a free water surface, grass covered soil and sand (B), 
the increased evaporation from soil 60" deep as compared with soil 
40" deep (C), and the difference in evaporation between grass cov- 
ered soil, bare soil and bare cultivated soil (D). 

The relations of annual rainfall to soil evaporation under various 
conditions are shown in Fig. 85, page 140. In each of these cases the 
annual rainfall is showm as abscissas and the corresponding evapora- 
tion by ordinates ; and if the annual evaporation were constant and 
approximately equal to the average, they would fall approximately 
on a horizontal line. These experiments show by their greater ap- 
proximation to the inclined lines, for each of which a mathematical 
expression (or formula) in terms of rainfall and evaporation can 
easily be derived (thus, the equation of the line A. B. (Diagram B) 
is E = 4 + .575 R) that in general soil evaporation increases with 
rainfall, which would normally be expected as the soil would as a 
rule be wet for a greater proportion of the time.* 



*It should be noted that the extension of the line shows an evaporation 
of 4 inches with zero rainfall which is evidently incorrect. A curved line 
passing through the origin of co-ordinates and approximating the line 
through the centers of gravity would agree better with theoretical conditions. 



142 



Atmospheric Moisture and Evaporation. 



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Evaporation from Soil. 1 43 

Certain general conclusions concerning annual evaporation can be 
drawn from these experiments as follows : 

1. Evaporation from soil increases with the rainfall. 

2. Evaporation from soil is less than from free water surfaces. 

3. Evaporation from sod is greater than from bare or cultivated 
soil. 

4. Evaporation from cultivated soil (uncropped) is less than from 
bare soil. 

5. Evaporation from deep soil is more than from shallow soil 
{both being underdrained). 

It should be noted, however, that there is a considerable departure 
in various experiments from either a fixed average or from the re- 
lations expressed by the straight inclined lines, and that any attempt 
to calculate the annual soil evaporation from the annual rainfall 
would in general be subject to large errors. This variation is due 
to the variation in the distribution of rainfall, temperature, vapor 
tension, wind velocities and other factors which are unknown and 
which even if known for these experiments would be impossible of 
exact expression as a whole especially as regards distribution of 
rainfall and periods of frozen ground. 

Certain important conditions not covered by the experiments 
previously discussed arise when land is without adequate drainage 
and the ground water is maintained at or near the surface by inflow 
from the surrounding drainage area, in the case of swamps, or from 
underground flows as in the case of various Western rivers in which 
there is no surface flow for considerable periods (as in the case of 
the Platte, Arkansas and Rio Grande Rivers). An important series 
of experiments were undertaken at the Denver Irrigation Field 
Laboratory in 1916 on evaporation from river bed materials under 
the conditions described above. 23 In these experiments which ex- 
tended over a three-month period the various materials were placed 
in tanks two feet in diameter and the water maintained at certain 
fixed distances below the surface. The resulting evaporation from 
the tanks was compared with the evaporation from a free water 
surface in a similar tank containing a depth of 3 feet of water. This 
comparison seems to give the experiment a wider significance than 
otherwise would be the case. On account of the limited funds 
available, more extended experiments were made on laboratory soil 



23 See "Evaporation from the Surface of Water and River Bed Materials," 
R. B. Sleight, Jour. Agric. Research, Vol. X., No. 5. 



1 44 Atmospheric Moisture and Evaporation. 

and on Cherry Creek sand than on the other river bed materials, 
and as the results seem entirely consistent the probable results 
under other relations of saturation of the river bed material can be 
judged with a considerable degree of accuracy. It should be noted 
that the laboratory soil was not washed materials, as in the case of 
the river bed materials, and therefore gives a better criterion of 
evaporation from undrained normal soils. The results of these ex- 
periments are shown in Fig. 86, and Fig. 87 shows the results of a 
mechanical analysis of the materials used. From a comparison of 
these diagrams it will be noted that evaporation seems to decrease 
with depth more rapidly with the coarser materials or with the 
capillary power of the soil. In this connection it is worthy of note 
that the effects of capillarity have been found by various experiments 
to be approximately as follows : 

TABLE 8. 

Character of Soil Capillary Limit Authority 

Feet 

Coarse Sand 4 Burr, Herring & Fuller 

Find Sand 8 Burr, Herring & Fuller 

Sandy Soil (moist) 5.5 Briggs and Lapham 

Sandy Soil (moist) 4 to 6 Stewart 

Fine Deep Desert Soil 25 Whitney 

75. Effects of Vegetation. — The nature and extent of the vegeta- 
tion on a surface have a marked effect on the amount of moisture deliv- 
ered to the atmosphere from the soil. Experiments at the Wiscon- 
sin Agricultural Experimental Station show that barley, oats and corn 
require 13.2, 19.6 and 26.4 inches of rainfall, respectively, to produce 
a crop. (See Table 9). This includes the transpiration and evaporation 
from the cultivated surface as well as the actual quantity used by vegeta- 
tion which is, of course, very small. The water simply serves to convey 
the soluble foods of the soil to the various fibres of the plant. The 
actual amount of water used in irrigation is not a fair criterion of the 
amount needed for the development of plant life as in most cases crops 
are over-irrigated. The actual depth of the rainfall and irrigation 
water used on crops varies from as low as twelve inches to several feet,, 
frequently running into quantities much in excess of any ordinary 
rainfall in moist climates where irrigation is found to be unnecessary. 

In the Report of the Kansas State Board of Agriculture for Decem- 
ber 31, 1889, Mr. W. Tweeddale, C. E., gives Table 10 containing the 
results of investigations by M. E. Risler, a Swiss observer, upon the 
daily consumption of water by different kinds of crops. 



Evaporation from Soils. 



145 




2 4 6 8 10 IZ 14 16 /# ZO 22 24 26 28 30 32 34 36 38 40 42 44 46 48 SO 52 
Depth to IVaterTctb/e — Inches below Surface 

Fig. 86.— Evaporation from River Bed Materials. 



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Hydrology — 10 



46 



Atmospheric Moisture and Evaporation. 



TABLE 9. 

The Amount of Water Required in Wisconsin to Produce a Pound of Dry 

Matter for Oats, Barley and Corn. 



Lbs. of 
water 

used 



Lbs. of 

dry- 
matter 
produced 



Lbs. of water per lb. Comput 
of dry matter 



ed yield 
per acre 



Computed 
amount 

of 
water 



Barley 1 

Barley 2 

Oats 1 

Oats 2 

Cor n 1 

Corn 2 



158.3 

141.03 

224.25 

220.7 

300.45 

298.65 



.3966 
.3488 
.4405 
.4471 
1.0152 
.9727 



399.14 
404.33 
509.31 
493.63 
295.95 
307.03 



Mean. 
401.74 



501.47 



301.49 



Lbs. 



7,441 



8, 861 



19,845 



In 
Inches 



13.19 



19.60 



26.39 



Mr. Tweeddale finds that this table agrees with careful experiments 
made in France and elsewhere, and calculates from it that from seed 
time to harvest cereals will take up fifteen inches of water and grass 
may absorb as much as thirty-seven inches. 

TABLE 10. 
Daily Consumption of Water by Crops 

Inches of Water. 
Crops. Minimum. Maximum. 

Lueern grass 0.134 0.267 

Meadow grass 0.122 0.287 

Oats 0.140 0.193 

Indian Corn < 0.110 1.570 

Clover 0.140 

Vineyard 0.031 0.035 

Wheat 0.106 0.110 

Rye 0.091 

Potatoes 0.038 0.055 

Oak trees 0.030 0.038 

Fir Trees 0.020 0.043 

The amount of moisture supplied to the air by forests is accomplished 
by several means : 

a. Transpiration of soil water by the trees. 

b. Direct evaporation of rainfall caught by the trees. 

c. Evaporation from the soil of the forest bed. 

Estimates for amount of transpiration can necessarily be only very 



Effects of Vegetation. 1 47 

roughly approximated since it depends upon a large number of variable 
factors such as the amount of water at the disposal of the plant, the 
stage of its development, nature and amount of foliage, temperature, 
humidity, amount of sunlight, condition of soil and the weather condi- 
tions. 24 

Mr. W. Harrington 25 made an estimate of the quantity of water re- 
turned to the atmosphere by various kinds of vegetation based on the 
observations made by Wollny and others. At the locality in which the 
investigation was made the transpiration was concluded to be 6.5 inches 
during the same period the evaporation from free water surface was 
8.39 inches. The transpiration was therefore yy% of the open water 
evaporation in this case. 

From observations of rainfall under shelter of trees it has been con- 
cluded that the rainfall reaching the ground is on the average about 
70% of that caught in the open. There was then 30% of the rainfall 
held by the trees which was directly re-evaporated, equivalent to 61% 
of open water evaporation for purposes of this estimate. The evapora- 
tion from the soil of the forest bed under the litter is according to vari- 
ous investigators from 13% to 67% of that from open water. 

The total moisture added to the atmosphere through the influence of 
the forest compared with the evaporation from free water surface is 
given as : 

Transpiration 77% of open water evaporation 

Direct Re-evaporation 61% of open water evaporation 
Forest Soil Evaporation 13% of open water evaporation 

Total 151% of open water evaporation 

For different kinds of vegetation, Table 11 based upon the investi- 
gation of Woolny, is of interest : 

TABLE 11. 

• Water Returned to Atmosphere 
Kind of Vegetation Proportion of Evaporation 

from Open Water 

Sod 192% 

Small Grain 173% 

Forest 151% 

Mixed Crops 144% 

Bare Soil 60% 

Zon 26 considers forests as the greatest evaporators of water, ex- 
ceeding all other vegetable coverings and even exceeding the evapo- 

24 Report Chief of Forestry Division, 1889. B. E. Fernow. 

25 Forest Influences, TJ. S. Dept. Agr. Forestry Div., Bui. 7. 

26 Science, Vol. 38, p. 71. 



1 48 Atmospheric Moisture and Evaporation. 

ration from water surfaces. He quotes Otozky, a Russian soil physi- 
cist, as estimating the amount of transpiration from forests as nearly 
equal to the annual precipitation and is of the opinion that if the At- 
lantic Plain and the Appalachian regions were deforested it would 
have a perceptible influence on the humidity and consequently on the 
rainfall of the Central States and the prairie regions to the westward. 

Tables 10 and 1 1, however, seem to indicate reasons for entirely differ- 
ent conclusions and to show that a decrease of stream flow may follow 
the destruction of forests and their replacement by meadows and culti- 
vated fields on account of greater evaporation resulting therefrom. It 
is quite evident on the basis of these tables that if the drainage areas are 
covered by grasses or cereals, there might be comparatively little water 
left for the flow of streams. Observations in Wisconsin 27 indicate 
that little change occurs in the flow of streams after deforestation or 
after considerable drainage operations, but that about the same amount 
of water is vaporized by the second growth and the crops or other vege- 
tation on deforested or drained areas. The character of the vegeta- 
tion on a drainage area and its physical condition may however exert 
considerable influence on the amount of vapor that reaches the atmos- 
phere. 

The presence or absence of forests, as shown by observations in 
Germany, has also a marked effect on evaporation, directly from the 
ground or from ponds or lakes within the forested areas. From these 
observations Prof. M. W. Harrington' s has compiled Fig. 88, 
page 149, which shows the effect on monthly evaporation. The upper 
curve represents the evaporation from water surfaces in the open coun- 
try, while the lower curve shows the evaporation from water surfaces 
within forests. The shaded area thus shows the reduction in evapo- 
ration due to the protection of the forest. 

76. General Principles. — Professor Cleveland Abbe 29 gives the 
following relations of evaporation, as established by Professor 
Thomas Tate : 

(a) Other things being the same, the rate of evaporation is nearly 
proportional to the difference of the temperature indicated by the wet- 
bulb and dry-bulb thermometers. 



29 Preparatory Studies for Deductive Method in Storm and Weather Predic- 
tion, by Prof. Cleveland Abbe. Annual Rept. Chief Signal Officer for 1889, 
Part I, Appendix 15. 

27 The Flow of Streams and Factors that Modify it, by Daniel W. Mead, 
Bui. 425 of the University of Wisconsin. 

28 Bulletin No. 7, U. S. Dept. of Agricluture, p. 97. 



General Principles. 



49 



(b) Other things being the same, the augmentation of evaporation 
due to air in motion is nearly proportional to the velocity of the wind. 

(c) Other things being the same, the evaporation is nearly inversely 
proportional to the pressure of the atmosphere. 

(d) The rate of evaporation of moisture from damp, porous sub- 
stances of the same material is proportional to the extent of the sur- 
face presented to the air, without regard to the relative thickness of the 
substances. 

(e) The rate of evaporation from different substances mainly de- 
pends upon the roughness of, or inequalities on, their surfaces, the 
evaporation going on most rapidly from the roughest or most uneven 
surfaces ; in fact, the best radiators are the best evaporizers of mois- 
ture. 




Fig. 88. — Reduction in Evaporation from Water Surface Due to the Presence 
of Forests (see page 148). 



(f) The evaporation from equal surfaces composed of the same 
material is the same, or nearly the same, in a quiescent atmosphere, 
whatever may be the inclination of the surfaces ; thus a horizontal 
plate with its damp face upward evaporates as much as one with its 
damp face downward. 

(g) The rate of evaporation from a damp surface (namely a hori- 
zontal surface facing upward) is very much affected by the elevation 
at which the surface is placed above the ground. 

(h) The rate of evaporation is affected by the radiation of surround- 
ing bodies. 

(i) The diffusion of vapor from a damp surface through a variable 
column of air varies (approximately) in the inverse ratio of the depth 
of the column, the temperature being constant. 

(j) The amount of vapor diffused varies directly as the tension of 
the vapor at a given temperature, and inversely as the depth of the 
column of air through which the vapor has to pass. 

(k) The time in which a given volume of dry air becomes saturated 



1 50 Atmospheric Moisture and Evaporation. 

with vapor, or saturated within a given percentage, is nearly independ- 
ent of the temperature if the source of vapor is constant. 

(1) The times in which different volumes of dry air become saturated 
with watery vapor, or saturated within a given per cent, are nearly 
proportional to the volumes. 

(m) The vapor already formed diffuses itself in the atmosphere 
much more rapidly than it is formed from the surface of the water. 
(This assumes, of course, that there are no convection currents of air 
to affect the evaporation or the diffusion). 

77. Measurements of Atmospheric Moisture and Evaporation. — 
The measurement of moisture in the atmosphere is accomplished by 
means of various forms of hygrometers and psychrometers, which, to- 
gether with their use, are described in various meteorologies. 30 Some of 
these forms are in use at all of the regular stations of the U. S. 
Weather Bureau. 

As the determination of evaporation by the Psychrometer is only 
roughly approximate and such evaporation also varies widely from 
year to year with other meterological conditions, it frequently becomes 
desirable for the engineer to determine from actual observations the 
evaporation which must be expected in connection with storage or 
other projects. Such experiments are usually made with round or 
square metallic pans of various depths placed either on or over the 
ground, or supported in the water and protected from waves in a 
suitable manner. 

Milham says 31 "The amount of evaporation is usually determined by 
exposing large pans in the open and measuring the amount evaporated 
in a given time. These pans should have large area and considerable 
depth, so that the temperature will ( be approximately the same as the 
temperature of the surrounding areas." 

Moore 32 illustrates an instrument designed by Prof. C. F. Marvin 
for use of the Weather Bureau. It consists of a large tank nearly filled 
with water, which is maintained at constant level by float on the sur- 
face of an auxiliary still basin communicating with the large tank by 
siphon. Whenever as much as .05 m.m. of water has evaporated, the 
fall of the float operates electrically to open a valve and admit just 



so See Meteorology, by W. I. Milham, pp. 197-203; Modern Meteorology, by 
Frank Walsh, pp. 141-145; Elementary Meteorology, by W. M. Davis, pp. 147- 
149; Meteorology, by Thos. Russell, pp. 34-38. 

31 Meteorology, by Milham, p. 193. 

32 Descriptive Meteorology, by Moore, p. 213. 



Measurement. 1 5 1 

enough water to restore the normal level. The quantity of water ad- 
mitted is measured by an electrically recording tipping bucket, similar 
to those used in recording rainfall. Observations at Kingsburgh, Cali- 
fornia 33 by C. E. Grunsky, were made by use of pans, three feet square, 
fifteen inches deep and water maintained about 5" below top of sides 
by replenishing when water had fallen about one-fourth inch, by using 
a calibrated measuring vessel. The pans were made of galvanized 
iron, a peg tapering to a point in the center of each pan extending up 
to the water surface. Two pans were used, one floated in the river, 
the other on land with sand banked around it to height of the water 
surface. 

It has been found that the size, location and exposure of the pan have, 
as shown in foregoing sections, a considerable effect on the amount of 
evaporation, allowances for which must be made in order that such ob- 
servations may be comparative. Biglow has found that there is a 
material difference in evaporation which will obtain from various sized 
pans, due partially at least to the more rapid removal of the vapor bank 
from the smaller vessels by the wind, and that the relations between 
evaporations from a lake surface and from pans of various sizes and 
locations are essentially as shown on Table 12. It seems doubtful that 
this table can be taken as the last word in regard to this evaporation re- 

TABLE 12. 

Evaporation Relations between Lake Surfaces ajid Pans of Various Sizes and 

Locations^ 

Size and Location of Pans Percentage of 

Evaporation 

Lake Surface 100 per cent. 

Land Pans 2 feet square 175 per cent. 

3 feet square 162 per cent. 

4 feet square 150 per cent. 

6 feet square 130 per cent. 

Floating Pans 2 feet square 140 per cent. 

3 feet square 130 per cent. 

4 feet square 120 per cent. 

6 feet square 104 per cent. 

lation, but it simply indicates the present status of the knowledge of this 
subject. 



33 Eng. News. Aug. 13, 1908. 

si See American Civil Engineers' Pocket Book (second edition, 1912), p. 1250; 
also Trans. Am. Soc. C. E., Vol. 80, 1916, pp. 1843-1858. 



! 52 Atmospheric Moisture and Evaporation. 

It would seem that not only the size of the pan,, but that its material, 
depth and color would have a considerable effect upon the evaporation 
results, and in each instance evaporation percentage should be estab- 
lished only after a careful consideration of the conditions in detail. 
Observations should also be made of atmospheric and water tempera- 
tures, wind movements and absolute humidity. Unfortunately, the ob- 
servations which are made and published are often deficient in the es- 
sential data which would make them of general value for comparative 
purposes, and when used without such data they are often misleading. 

78. Importance of a Knowledge of Evaporation and Atmospheric 
Moisture in Engineering Studies. — The entire question of atmos- 
pheric moisture has an important bearing on the problems of distribu- 
tion and local intensity of precipitation, and a knowledge of this sub- 
ject is requisite for a proper understanding of rainfall which is of 
great importance to the engineer. It should be noted that water vapor 
under similar conditions of temperature and pressure is lighter than 
air and that moisture laden air is lighter than dry air (see Sec- 
tion 61) ; hence there is a decided tendency for the moist air near 
the land or water surface to rise through the drier and heavier upper 
air strata. It should also be noted that as the amount of moisture in 
each unit of air at the equator is six times the amount in each unit at 
the poles, the air at the equator is lighter than the air at the poles on 
account of its contained moisture as well as its higher temperature, and 
thus serves to increase pressure differences and consequent general at- 
mospheric circulation. 

Evaporation and transpiration also have important effects on stream 
flow as will be discussed in a later chapter, and their influence must be 
understood for a correct appreciation of many problems of water sup- 
ply. A knowledge of evaporation is of direct importance to the en- 
gineer in the investigation of storage projects, water supplies for 
canals, etc., as the net amount of water which can be retained by reser- 
voirs, or will be needed for canals, is profoundly influenced by the 
evaporation which will take place during the year or the period of use. 
As previously noted (see Section 65) the monthly evaporation from 
free water surfaces in many parts of the United States is equal to or 
greater than the monthly rainfall in the same area; hence the water 
available in any reservoir will be the difference between the runoff 
from the drainage area which feeds the reservoir, plus the rainfall on 
the reservoir surface, less the evaporation from such surfaces, plus 
other losses such as percolation, etc., and less any amounts abstracted 



Importance in Engineering. 



53 



for use. A minimum exposure of surface to evaporating effects is 
therefore usually essential to economic storage ; that is to say to 
eliminate evaporation so far as practicable at the reservoirs there 
should be the greatest practicable depth. A study of the effect of 
areas on the water supply which might be secured each month from 
an Eastern stream in a reservoir having an area equal to the vari- 




1894 1895 1896 1897 1898 

Fig. 89. — Cumulative Storage as Modified by Evaporation from Reservoirs of 
Various Relative Areas. 



ous percentages of the drainage areas, from which the water is re- 
ceived, is shown in Fig. 89. 

79. General Conclusions. — The study of evaporation has not as yet 
been carried far enough to warrant any definite general conclusion 
which can be reduced to a formula by means of which the monthly or 
annual evaporation at any locality and under definite conditions of ex- 
posure can be calculated from the Weather Bureau data for tempera- 
ture, humidity and wind movements. Nevertheless sufficient informa- 
tion is available that by a study of the conditions and the results of 
the various experiments together with the Weather Bureau records, 
rough approximations can be made which will give an idea of the ex- 
treme variations which are liable to occur. As in all other engineering 
calculations, an allowance for ignorance of this subject must be made 
by factors of safety, the magnitude of which may perhaps be decreased 
with further study and investigation. 



1 54 Atmospheric Moisture and Evaporation. 

LITERATURE 

Adiabatic Changes of Condition of Moist Air, Dr. Otto Neuhoff. In Mechan- 
ics of the Earth's Atmosphere, p. 430. Translated by Cleveland Abbe, 
Smithsonian Institution, 1910. 
Vertical Temperature Gradients of the Atmosphere. Bui. Mt. Weather Ob- 
servatory. Also Weather Rev. Sup. No. 3, 1916, on Aerology. 

Amount and Vertical Distribution of Water Vapor on Clear Days, W. J. 
Humphreys. Bui, Mt. Weather Observatory, Vol. 4, part 3, 1911. 

Psychrometric Tables for Obtaining Vapor Pressure, Relative Humidity and 
Temperature of the Dew Point, U. S. Weather Bureau, No. 235, 1900. 

Temperatures and Vapor Conditions of the United States. U. S. Weather 
Bureau, Bulletin S., 1909. 

On Evaporation and Percolation, Charles Greaves. Proc. Inst. C. E., 1875-76, 
Vol. 45, p. 19. 

Evaporation, Desmond Fitzgerald. Trans. Am. Soc. C. E., Vol. 15, p. 581. 
Sept. 1886. 

Loss of Water from Reservoirs by Seepage and Evaporation, Bulletin No. 45, 
Colo. Agric. Expt. Sta., Fort Collins, Colo. May, 1898. 

Depth of Evaporation in the United States, Monthly Weather Review. Sep- 
tember, 1888. 

Depth of Evaporation in the United States. Eng. News, Dec. 30, 1888; Jan., 
1889. 

Relation of Evaporation to Forests, B. E. Fernow. Bui. No. 7, Forestry 
Div., U. S. Dept. Agric. and Eng. News, 1893, Vol. 30, p. 239. 

Evaporation Observations in the United States, H. H. Kimball. Read before 
The Twelfth National Irrigation Congress, 1904; Eng. News, April 6, 
1905. 

Measurement of Soil Evaporation under Arid Conditions. Eng. News, Vol. 
66, Oct. 12, 1911, p. 428. From Los Angeles Co. Bureau of Water Supply, 
Chas. H. Lee. 

Method of Estimating Amount of Evaporation from Water and Soil Surfaces 
in Livermore Valley, Cal. Eng. Cont, Apr. 30, 1914, and May 7, 1913. 

California Evaporation Records, Edwin Duryea. Eng. News, Feb. 29, 1912. 

Loss of Water by Seepage and Evaporation, Ferre Canal, W. B. Gregory, 
Jour. Assn. Eng. Soc, July, 1912. 

Evaporation from Irrigated Soils, Samuel Fortier. Eng. News, Sept. 5, 1912. 

Evaporation from Salton Sea, C. E. Grunsky. Eng. News, Aug. 13, 1908. 

Evaporation Observations in U. S., H. H. Kimball. Eng. News, Apr. 6, 1905. 

An Apparatus for Measuring Evaporation in Freezing Weather, E. Kuichling. 
Eng. Rec. July 31, 1897. 

Evaporation Losses in Irrigation, Samuel Fortier. Eng. News, Sept., 1907. 

Records of Evaporation Tables at 23 Different Stations in Various Parts of 
the United States. Eng. News, June 16, 1910. 

The Losses of Water from Reservoirs of Seepage and Evaporation, L. R. Car- 
penter. Bui. 45, State Agricultural College, Ft. Collins, Colo. 

Evaporation Losses in Irrigation and Water Requirements of Crops, Samuel 
Fortier, O. E. S. Bui. 177, 1907, U. S. Department of Agriculture. 



Literature. 155 

Studies of the Evaporation of Water over Lakes and Rivers, Prof. F. H. Bige- 

low. Weather Review, July, 1907, Feb., 1908, and Summary, 1908, Feb., 

1910, July, 1910. 
Evaporation from the Surface of Water and River Bed Materials, R. B. Sleight, 

Jour. Agric. Research, Vol. 10, No. 5, 1917. 
Forecasting the Water Supply in California, A. G. McAdie. Month. Weath. 

Rev., March, 1911, and July, 1913. 
Water Supply of San Bernardino Valley, J. B. Lippincott. 19th Annual Rept. 

U. S. G. S., part 4, 1898, p. 624. 
Some Field Experiments on Evaporation from Snow Surfaces, F. S. Baker. 

Month. Weath. Rev., July, 1917, p. 363. See also Sept., 1915, p. 486. 
Water Resources of a Part of Owens Valley, Chas. H. Lee. Water Supply 

Paper No. 294, 1912. 
Condensation upon and Evaporation from a Snow Surface, B. Rolf. Month. 

Weath. Rev., Sept., 1915. Also Science Abstracts Sec. A, Sept. 25, 1915. 
The Disappearance of Snow in the High Sierra Nevada of California, A. J. 

Henry. Month. Weath. Rev., March., 1916. 
See also references on Evaporation from Soils given in Table 7, page 142. 



CHAPTER VII 

PRECIPITATION 

80. Precipitation — The Ultimate Source of all Water Supplies. — 

All available water supplies, including the surface waters of lakes and 
swamps, the water flowing on the surface and in brooks, creeks and 
rivers, the waters of springs, the waters standing in or flowing through 
the subterranean strata, including all waters available for agriculture, 
for public and private water supplies, for irrigation, for water power, 
for navigation and for other purposes, are derived primarily from pre- 
cipitation. Deficient precipitation, or rainfall much below the aver- 
age, may result in insufficient supplies for any or all of these purposes 
unless the shortage has been duly foreseen and provided for by suitable 
engineering construction. On the other hand, a super-abundance of 
rainfall may produce undesirable conditions. When heavy rains occur 
in a short period of time, they frequently produce disastrous floods and 
overflow conditions which may be seriously detrimental to human in- 
terests. Even normal rainfall may be locally injurious when lands are 
level and drainage conditions are imperfect, or when lands receive ex- 
cess drainage from higher surrounding lands or overflow from streams 
which may inundate or saturate them temporarily or permanently and 
render them more or less unsuitable for agriculture or other utilitarian 
purposes. Under these conditions the successful reclamation of such 
lands may make systems of drainage ditches or of levees and other en- 
gineering works essential for protection. 

In all of the problems of the hydraulic engineer, arising from a de- 
ficiency or a superabundance of water, or from the necessity or desira- 
bility of utilizing the water resources of a country in various ways and 
for various purposes, the questions of the quantity of rainfall and of 
its occurrence, distribution and influence are fundamental to such prob- 
lems and of great importance in their solution. Many of the problems 
with which the hydraulic engineer has to deal are directly affected by 
precipitation ; and in many other cases, the influence is indirect but 
important. The subject of precipitation, therefore, deserves careful 
study and investigation. 

81. The Practical Consideration of Rainfall. — The engineer is par- 
ticularly interested in rainfall as it affects surface water or runoff and 



Practical Considerations. 1 57 

ground water or underflow, and especially in the maximum and mini- 
mum intensities and quantities of flows which have occurred in the 
past, and which must therefore be anticipated in the future from given 
drainage areas or from given ground water sources. The rainfall and 
its distribution affect questions of climate, sanitary conditions, agri- 
culture, irrigation, drainage, public and private water supplies, water 
power, flood protection, river regulation, internal navigation, and many 
other problems with which the engineer has to deal. While rainfall is 
only one of numerous factors in most of these problems, it is an impor- 
tant one for without rainfall there would be no runoff or underflow, 
and there could be no animal or vegetable life. 

■ If accurate long time and detailed records of local rainfall are avail- 
able, conclusions as to the rainfall conditions that may occur in the 
future are best answered by the consideration of those known to have 
occurred in the past, that is by the actual rainfall records of the local- 
ity. Records sufficient in extent for entirely satisfactory use are sel- 
dom available, as few records are of great length, and those few are 
often considerably in error. 

When extended local records are not available, the answer to the 
questions of the probable future rainfall conditions becomes more dif- 
ficult and can be answered only by a careful and extended study of the 
rainfall conditions in other localities, with due allowance for the great 
differences which are liable to exist in local conditions. 

In the study of rainfall data, details are essential and generalizations 
are of little value. For hydrological study, variations in yearly rain- 
fall and the varying distribution throughout the various years are of 
greatest importance. Averages are only of general interest. The 
questions of the frequency in occurrence of periods of extreme rain- 
fall, either maximum or minimum, and the rate and distribution of 
rainfall for such periods, are matters of importance in both engineer- 
ing and agriculture. If rain commonly occurs in adequate amounts 
at times when most needed and under conditions where it can be best 
utilized, it becomes an asset of great value ; whereas if it occurs at 
seasons when it cannot be utilized or under unfavorable conditions of 
intensity and distribution, it may become of serious import. 

The influence of rainfall on the flow of streams and on ground water 
is so direct that those unfamiliar with the subject are apt to assume 
that the relation may be represented by some simple expression and 
that, therefore, if the rainfall for a period of years be known, the cor- 



1 58 Precipitation. 

responding stream flow and the amount of water available in the un- 
derflow, may be directly and readily calculated therefrom. Upon ac- 
quiring only a brief familiarity with the subject it becomes evident that 
no such simple relation exists and that the relationship is in fact com- 
plicated by a multiplicity of other physical conditions which have an 
important if not an equal influence. 

Observations of stream flow are quite limited both in time and geo- 
graphical extent, while the observations of rainfall have extended 
over a considerably greater period of time and the points of observa- 
tion of rainfall are also geographically much more widely distributed. 
If, therefore, it is possible to trace any relationship between the flow of 
streams or of the underflow of ground water and the rainfall and other 
physical conditions on the drainage areas that will enable the engineer 
to calculate or estimate the stream flow even approximately, such re- 
lationships become of great value to the hydraulic engineer on account 
of the lack of other more definite information. It is therefore impor- 
tant that the engineer inform himself as fully as possible on the rela- 
tions that exist between rainfall and stream flow and the modifications 
of those relations by other physical factors. By such means the in- 
formation regarding recorded rainfall, sometimes available for long 
terms of years, may be applied to the problem of stream flow and 
ground water supply, in which the engineer is often directly concerned. 

The engineer is frequently obliged to draw conclusions of greater or 
less importance, often from very inadequate data, as to rainfall and 
the resulting ground water supply or surface runoff, and their possible 
extremes from some given source or drainage area. In such cases, the 
engineer may be obliged to estimate the probable and possible rainfall 
conditions from comparisons with other areas where such data, also 
frequently inadequate, are available and which areas are similarly lo- 
cated geographically, topographically and meteorologically, and where, 
on account of such similarity of location and conditions, similar inten- 
sity and magnitude of rainfall may reasonably be anticipated. 

It is readily demonstrable that local conditions are never exactly du- 
plicated, and that any comparisons between apparently similar localities 
are subject to possible errors of considerable magnitude. Hence, esti- 
mates of rainfall and runoff, and the design of structures based on 
these comparisons, must for safety be made with these probable errors 
in mind, and must include factors of safety proportional to the possible 
casualties which might result from designs based on such erroneous 
data. 



Practical Consideration. 1 59 

In considering these problems it is important to recognize that gen- 
eral principles are frequently subject to wide variations, and even to 
marked exceptions, especially when relating to the complicated subject 
of meteorology. It is highly essential therefore in assuming that any 
general principles may or will obtain in a given locality, to secure suf- 
ficient data to demonstrate that all conditions are favorable to the 
probable prevalence of such principles and the probable force or in- 
tensity of the phenomena resulting thereunder. It must also be re- 
membered that only limited conclusions should be drawn from limited 
observations. In many cases, conclusions based on data for single 
months or years would be entirely reversed if based on observations 
for other periods of equal length, and both would be altered if based 
upon the average or extremes shown by long series of observations. 

In these various questions of engineering importance, even the best 
information is generally incomplete and unsatisfactory. The rule to 
be followed is to make all investigations as complete as permissible and 
to limit assumptions so far as possible. On account of its great im- 
portance to the engineer, the subject of rainfall is therefore discussed 
in as much detail as space will permit. 

82. Causes Which Produce or Influence Precipitation. — A discus- 
sion in anything like adequate detail, of the causes which produce pre- 
cipitation and which influence its distribution, its total amount, and its 
variation, would be too extended for our purpose. From their very 
nature, great uncertainty is involved in these questions, for the factors 
are not only world wide but probably involve influences which relate to 
the whole solar system, or at least to direct solar influences on the at- 
mospheric conditions of the earth. It is probable that this subject will 
never be understood in detail, but long observations and study will 
undoubtedly greatly extend human knowledge of the principal factors 
and their most important influences. 

In general, the source of precipitation is the water taken up by 
evaporation from wet surfaces. The immediate vicinity of large bod- 
ies of water from which the most extensive evaporation necessarily 
takes place, and of extended areas of vegetation from which great 
quantities of water are transpired during periods of development and 
growth, are, therefore, the most important requisites for extensive pre- 
cipitation. In general, distance from extensive sources of supply re- 
sults in a decrease in annual precipitation. These conditions are, how- 
ever, greatly modified by the direction of the wind, which, as has been 
pointed out, is largely dependent at least for a considerable portion of 



1 60 Precipitation. 

the earth's surface, on atmospheric pressure and the passage of the 
great centers of cyclonic atmospheric movements around the globe. 
The present opinion of meteorologists on the subject of causes of rain- 
fall is set forth by Blanf ord as follows : 

"As a result of a long study of the rainfall of India, and perhaps no 
country affords greater advantages for the purpose, I have become con- 
vinced that dynamic cooling, if not the sole cause of rain, is at all 
events the only cause of importance, and that all of the other causes 
so frequently appealed to in popular literature on the subject, such as 
the intermingling of warm and cold air, contact with cold mountain 
slopes etc., are either inoperative or relatively insignificant." x 

The ascensional movement of moist air which results in dynamic 
cooling, and consequently in precipitation is brought about in one of 
three different ways : 

(i) By convective currents. 

(2) By hills and mountains. 

(3) By cyclonic circulation. 

Curtis - classifies rainfall as convective, orographic or cyclonic, ac- 
cording as it is due to the first, second or third of these causes of as- 
censional movement. In some cases two or all of these causes may be 
operative at the same time. 

1. Under conditions of purely convective rainfall, the heat and mois- 
ture of the atmosphere cause the circulation to be primarily vertical, 
and the local evaporation is largely precipitated without being carried 
away by horizontal currents. In such cases increased evaporation will 
result in an increased rainfall and any change in surface condition 
which increases or diminishes the evaporation will, under such a con- 
dition, be followed by a corresponding increase or decrease in precipi- 
tation. 

Curtis says : "The equatorial rain belt is the most prominent region 
with almost exclusively convective rainfall. The Brazilian forest re- 
gion, the Aruwhimi district of central Africa, the Malaysian Archi- 
pelago, and the valley of Upper Assam in India are in or near this 
belt. They have light winds, and the moisture evaporated from the 
surface is precipitated before being carried to any considerable distance 
by horizontal currents. Under these conditions an increase or de- 



1 Nature, Vol. XXXIX, p. 583. 

2 Analysis of the Causes of Rainfall, G. E. Curtis. Forest Influence. Bui. 
No. 7, Forestry Division U. S. Dept. Agriculture, p. 187. 



Causes of Precipitation. 161 

crease in the evaporation will be followed by an increase or decrease 
in rainfall. * * * 

"Blanford estimated that for the Aruwhimi district probably over 
half of the rainfall is due to the direct restoration of the moisture 
evaporated. * * * 

"Bordering on each side of the equatorial belt are the regions of th*i 
trades, which, over the ocean, are almost rainless ; but over intercept- 
ing land areas, such as Central America and the Antilles, considerable 
rainfall occurs. This is frequently difficult to analyze, but it is 
largely convective and in hilly regions partly orographic. The sea- 
sonal distribution shows that the rainfall is intimately related to the 
annual oscillation of the limits of the trade-wind, and that the rainy 
season requires a special explanation. With the exception of the well 
known tropical cyclones of the seas, the distribution of pressure over 
the trade region is unfavorable to the development of a cyclonic circu- 
lation, and consequently, cyclonic rainfall is seldom presented." 

2. Under conditions of orographic rainfall, horizontal moist air cur- 
rents are forced to rise by the hills or mountains that they encounter in 
their path. In such cases the moisture evaporated in the region lying 
to windward may be partially or entirely precipitated over the slope and 
the region to windward where the ascensional movement is developed. 
An increase in evaporation under such conditions may be restored to 
the basin by increased precipitation. The extent to which this restora- 
tion of moisture lost by evaporation will take place will depend on the 
topographical conditions and the frequency and direction of the winds. 

The heavy rainfalls on the Northern Pacific Coast of the United 
States and on the Southern Appalachians in North and South Caro- 
lina are examples of orographic rainfall. The rainfall on the Pacific 
Coast is due to the passages of cyclonic storms from the Pacific, and 
the rainfall of the Carolina highlands is largely due to the interception 
of the West India hurricane by the Southern Appalachian Mountains. 

3. The conditions of cyclonic rainfall include the great variety of 
rain types related to cyclonic circulation. This is the type of rainfall 
which is most common in the United States east of the Rocky Moun- 
tains. 

Moore 3 has pointed out the main controlling factors influencing rain- 
fall in the Eastern United States as follows : 

"Before one can get a comprehensive idea of the magnitude of the 



s Report on the Influence of Forests on Climate and on Floods, p. 20 — Gov- 
ernment Printing Office, Washington, 1910. 
Hydrology — 11 



62 



Precipitation. 




Causes of Precipitation. 1 63 

problem involved in the creation of floods of the United States, it will 
be necessary for him to first study Fig. 90, page 162 which gives a 
typical illustration of the cyclonic storms that frequently form on the 
Rocky Mountain Plateau, either on its northern, central, or southern 
portions. Under the influence of gravity air flows from regions where 
the pressure is great toward the regions where it is less. In the case 
illustrated by Fig. 90 the atmosphere, as indicated by the direction in 
which the arrows point, is flowing from the region marked "high," 
which is central over the Carolinas, toward the region where the pres- 
sure is low, which is central over Montana, and the vaporous atmos- 
phere that rises from the Gulf of Mexico and the adjacent ocean (and 
the marginal and interior lands — Author) is carried far into the in- 
terior of the continent. Conditions similar to these occur many times 
each month, and as a result, the eastern and central portions of the 
United States are bathed in a succession of rains which, as shown by 
Figs. 109, no and in, pages 201 and 204, gradually thin out and 
largely disappear on the eastward edge of the Rocky Mountain Plateau, 
because the currents of air from the Gulf of Mexico do not reach far- 
ther inland." 

Curtis says : "In the ordinary progressive area of low pressure the 
cyclonic circulation is largely horizontal, but with an upward com- 
ponent. This upward component produces the usual rainfall of our 
cyclonic storms. In these storms the horizontal component of the cir- 
culation is so large that the moisture evaporated over one region is 
precipitated over another. Consequently, in regions where rainfall is 
of this type, an increased evaporation in any region will not be fol- 
lowed by an increased rainfall in that same locality. 

"In the local thunder storms we have a type of rain related to a cy- 
clonic circulation in which the vertical component often becomes very 
large, as compared with the horizontal component. This predominat- 
ing vertical component is due to convection and the accompanying rain- 
fall is to be considered as partly or largely convective. Convection in- 
duces and initiates a cyclonic circulation which may continue after the 
direct convective action has ceased. * * * ' : 

83. Sources of Atmospheric Moisture. — The atmospheric vapor 
from which the rainfall is derived is replenished by evaporation 
from the free water surfaces of creeks, rivers, lakes, swamps and 
oceans, from the moist soil and other surfaces wet by precipitation, and 
from the transpiration of plants which draw their moisture from the 
soil waters, sometimes from many feet below the surface. 



1 64 Precipitation. 

The oceans which cover three-fourths of the surface of the earth are 
the chief source from which atmospheric moisture is derived and from 
which the precipitation of the earth as a whole is most largely furnished. 
The ocean is also the principal source of rainfall of the islands and of the 
lands adjoining the continental coasts especially those near the paths of 
cyclonic storms from the seas toward the lands. The precipitation on 
continental interior lands is, however, the phenomenon in which the en- 
gineers are more generally interested, and the source of this precipita- 
tion is derived most largely from the moisture that obtains from the 
continental evaporation, from land surface and from the surfaces of 
rivers, lakes and swamp areas, and indirectly by the transpiration from 
animal and vegetable life. By far the greatest portion of the rain fall- 
ing on continental areas is thus returned to the atmosphere, for the dis- 
charge of the rivers of a continent into the seas will not equal half of 
the continental rainfall. (See Table 13, page 165). 

While a certain portion of the amount of precipitation retained from 
the runoff sinks into the strata and, in some cases, may flow underground 
to the sea, thus neither appearing in runoff nor adding to atmospheric 
moisture, and a small amount of the rainfall is taken up and forms part 
of permanent vegetable and animal growth, yet these losses are com- 
paratively insignificant, and by far the greater portion of the rainfall 
not appearing as runoff is as a rule directly or indirectly evaporated into 
atmospheric moisture. 

From one-half to perhaps two-thirds of the average rainfall is there- 
fore probably evaporated into atmospheric moisture and unites with the 
ocean vapor in the great atmospheric storehouse of moisture from 
which rainfall is derived. 

The average rainfall of the United States is estimated at about thirty- 
six inches. From eighteen to twenty-four inches of this is probably 
re-evaporated and the difference, aggregating from twelve to eighteen 
inches, is supplied from the oceans and gulf waters which adjoin the 
country. 

When the moisture from the oceans is precipitated on the land closely 
adjoining the coast, on account of parallel mountain ranges (as in the 
case of the Sierra Nevada Mountains of the U. S.) and in consequence 
when the lands beyond the mountain ranges receive little moisture from 
the ocean, the evaporation from such lands is gradually moved eastward 
by the easterly atmospheric drift and the country must be a desert. 
Even when no mountains exist close to the ocean, the ocean moisture is 
usually precipitated not far from the coast line and" the precipitation on 



Geographical and Topographical Conditions. 1 65 

the interior is most largely derived from interior sources of evaporation. 
There is no doubt but that the precipitation along the coast is ultimately 
evaporated and moves inland with the succeeding storm movements 
while much evaporation from the land is carried to the sea in the same 
way. 

84. Geographical and Topographical Conditions Affecting Pre- 
cipitation. — While various causes may be active in the production of 
rainfall, by far the greater portion of precipitation is caused by the ex- 
pansive cooling of air as it ascends, due to cyclonic, orographic, or con- 
vective circulation, as produced by the passage of storm centers, the 
existence of mountain chains or the vertical currents of moist air dur- 
ing calms or within enclosed intermountain areas. 

TABLE 13. 

Approximate Average Rainfall, Runoff and Evaporation from Various Drain- 
age Areas 

Mean Mean Mean 
Drainage Area Rain- Run- Evapo- Evaporation 

fall off ration ^r^ <%Evap. 

•Great Lakes 1882-98 31.4 11.6 19.8 63 

Genesee River 1890-98 40.3 14.2 16.1 65 

Croton River, N. Y.. 1877-98 49.4 22.8 26.6 54 

Sudbury, Mass 1875-1900 46.1 22.6 23.5 51 

Neshaminy, Pa 1881-99 ' 47.6 23.1 24.5 53 

Hudson River 1888-1901 44.2 23.3 20.9 47.5 

Connecticut 1872-85 43.0 22.0 21.0 49 

Upper Mississippi .. 1892-95 24.6 3.6 20.99 85 

DesPlaines, 111 1896 39.6 6.7 32.9 83 

Platte, Neb 1894 12.8 1.0 11.8 92 

Wisconsin River . . . 1903-08 33.7 21.8 11.9 35 

Cbippewa River .... 1904-08 32.5 16.2 16.3 50 

St. Croix, Wis 1902-04 51.4 17.1 34.3 67 

Rock River, Wis. . . 1904-08 32.2 6.8 25.4 79 

Precipitation may therefor be greatly modified by the location of the 
area considered relative — 

a. To large bodies of water or other sources of vapor. 

b. To the tracks of cyclonic storms. 

c. To altitude, and especially to the presence of mountain ranges. 

It is especially important to recognize that these influences are interde- 
pendent, and that the effect of one element may so dominate or ob- 
scure the effect of others as to render them, even in extreme cases, 
largely insignificant. 



1 66 Precipitation. 

85. Precipitation in Relation to Location near Bodies of Water 
and Tracks of Cyclonic Storms. — Figs. 66, 67 and 68, pages 120 and 
121 show clearly the effect of the oceans and lakes on the absolute and 
relative humidity of the adjacent lands of the United States. The 
effects of distances from these sources of supply on local precipitation 
are also shown in general both by these same maps and by Fig. 109, 
page 201, which shows the mean annual rainfall of the United States. 

The removal of aqueous vapor by mountain heights, and the result- 
ing decrease in precipitation in areas beyond such elevations, are also 
illustrated by the area of the country just east of the western moun- 
tains. This area, although near an abundant source of supply, is prac- 
tically deprived of its value by the intervening mountain ranges. 

The small rainfall in southern California, in spite of its location close 
to the Pacific Ocean, illustrates the necessity of favorable wind cur- 
rents in order that adequate precipitation shall result. The precipita- 
tion in the area east of the Rocky Mountains rapidly decreases in quan- 
tity as the distance increases from the Gulf of Mexico and southern 
Atlantic, although the vapor is carried from these sources and from 
the moist land along their borders far into the northwest portion of the 
country by reason of the influence of the frequent slow passage of low 
areas of atmospheric pressure or cyclonic storm centers which cause 
the moist atmosphere to flow farther inland, but overcome distance 
only to a limited extent. In the case of Montana and the Dakotas, lo- 
cated within the track of the most numerous storms of the continent, 
the limited effect is not sufficient to produce rainfall equal to the average 
in the United States. In the southwest, the comparative freedom from 
the passage of these storm centers limits the atmospheric movements in 
a westerly direction and gives rise to semi-arid conditions, comparatively 
near to abundant sources of moisture. 

86. Occurrence and Distribution of Rain Storms. — The origin of 
cyclonic storms, which are one of the principal causes of precipitation, 
and the varying paths of the same across the United States, have been 
discussed in sec. 38 et seq. As the air expands and rises at and near 
the center of low pressure, a reduction in temperature occurs through 
direct contact and mixing with colder bodies of air, through direct 
radiation of heat to the surrounding space and especially through ex- 
pansion without material transmission of heat. As soon as the dew 
point is reached, clouds are produced which consist either of con- 
densed moisture or of even moisture congealed into minute crystals of 
ice. The clouds are ordinarily carried high in the atmosphere to the 



Occurrence and Distribution of Storms. 1 67 

northeast of the center of low pressure by the winds from the south 
which reach and join the cyclonic whirl. As the intensity of the cir- 
culation increases and moist air is drawn from humid sources with 
favorable conditions, these clouds thicken and become so dense by 
the resulting condensation of vapor that precipitation begins to in- 
crease in quantity at or near the center of low barometric pressure. 
These areas of precipitation are popularly stated to be in the soutn- 
west quarter of the minimum pressure area where perhaps the most in- 
tense precipitation may normally occur, but an examination of the 
weather maps shows that in few cases is precipitation confined to that 
locality. With the passage of the low or storm center, the rotating cy- 
clonic winds change in direction and the cold and usually dry winds 
from the northwest and north, begin to flow, taking up the moisture, 
and the clouds disappear with resulting clear and cooler atmospheric 
conditions. 

The above may be regarded as the general rule of purely cyclonic 
rainfall. The actual occurrence of rainstorms, however, is generally 
complicated by topographical and barometric conditions, and the gen- 
eral distribution of the rain is frequently far more extended than the 
above description would indicate. Examinations of the weather map 
seem to indicate that the rainstorm frequently follows in the general 
path of the cyclonic center long after its passage and even extends to 
and under the anti-cyclonic or high pressure center. The general law 
seems to prevail to a greater extent as the centers of low and high pres- 
sure increase in intensity. 

87. Effects of Altitude on Precipitation. — Mountains, and espe- 
cially mountainous ranges, as elsewhere noted, have a marked effect on 
atmospheric movements, and hence on precipitation. 

a. Mountains intercept the low lying, rain-bearing clouds. 

b. When located in the path of atmospheric movements, the lower 
prevailing winds are forced upward, giving rise to rapid cooling and 
hence to precipitation when the- winds are burdened with moisture. 

c. Mountains also cause local atmospheric circulation and consequent 
orographic rainfall. 

From the presence of clouds at 3,000 to 7,000 feet above sea level it is 
reasonably assumed that the dew point is most commonly attained in the 
atmosphere at these elevations, and for the same reason, that the greatest 
relative amount of rainfall ordinarily occurs at these altitudes. The rain- 
fall on lower elevations is supposed to be decreased somewhat by the 
evaporation of the raindrops falling through non-saturated air. In the 



1 68 Precipitation. 

arid portions of the country, apparently quite a heavy precipitation from 
a cloud may often be seen, when only a trace or perhaps no rain reaches 
the ground, all or nearly all of the water being evaporated during its 
fall. The author has been unable to find any data to substantiate the 
claim of a decrease in rainfall above the normal cloud elevations. 

The presence of mountains across the path of cyclonic atmospheric 
m'ovements causes an upward flow, a consequent cooling and a precipi- 
tation of the contained moisture which frequently affects the quantity 
of rainfall at higher altitudes and also at considerable distances to 
windward of the actual elevation. 

The altitude at which the maximum rainfall occurs is higher in sum- 
mer than in winter and occurs at an elevation of from 3,000 to 7,000 
feet. In the Alps, the maximum rainfall is found to occur at an alti- 
tude of about 4,000 feet in the winter, while during the summer the 
maximum rainfall occurs at an elevation greater than is covered by the 
records. 

The effect of the prevailing direction of moisture-laden winds modi- 
fies the general rule to a considerable extent since mountains thus have 
greater rainfall on the windward side than on the leeward side. This 
condition is perhaps best illustrated by the mountains of the northwest 
coast in which the rainfall increases rapidly with the elevation, but is 
much greater on the westward than on the eastward side. 

The plateaus of Southern Utah, which rise to an elevation of more 
than 10,000 feet, are apparently well watered as they support an exten- 
sive forest, while the surrounding lower country is practically a desert. 
This condition is shown on nearly all mountains of the United States, 
more strikingly perhaps upon the western mountains which for the 
most part are surrounded by semi-arid plains upon which trees may 
grow only along the water courses, while the mountains themselves are 
thickly clothed with forest growth above a certain altitude and nearly 
up to the region of perpetual snow. 

In the United States, the absence of records at the high elevations 
makes it impossible to determine with certainty the relation which 
exists between rainfall and altitude in any given region. It is known 
that the relation is not the same at different places, according as these 
localities are subject to the various influences of winds, neighboring 
topographical features, and other conditions which affect the processes 
of precipitation. 

That rainfall increases with altitude is a local and not a universal 
principle. That the rule is broadly true makes the general assump- 



Altitude. 1 69 

tion common and often misleading. In considering the amount of 
rainfall with respect to water supply, it is not safe to count on this 
principle in localities where it is not known to prevail, for in some cases 
no such increase is found, and in other cases even a decrease in rain- 
fall with altitude occurs. 

The attempt to establish formulas for such increase, unless such 
formulas are understood to be for very local and restricted use, is 
misleading and dangerous. The problem therefore must always be 
one of local study and investigation. 

88. Minor Influences. — The extent of the influence exerted upon 
the amount and distribution of precipitation by minor physical condi- 
tions is at best uncertain. The opinion that the presence of forests 
largely affected such distribution was formerly quite general and 
considerable data have been offered to sustain this hypothesis. The 
effects, if any, are within the limits of the errors of observation, and 
hence of little value as proof either for or against the assumption. 
Standing within the shade of a dense forest of mighty trees the 
assumption of their importance as a factor in the production of precip- 
itation may seem warranted, but if the same forest be viewed from 
a neighboring mountain top, its apparent insignificance in controlling 
or even influencing such vast atmospheric forces seems conclusive. 
Meteorologists have in general concluded that the presence or absence 
of forests has little or no influence in modifying rainfall. 4 The occur- 
rence of rain over the dense forests of -the Pacific Coast and in the 
tropics has been even lately advanced as an argument in proof of the 
effect of forests on rainfall under at least special conditions. It is 
evident, however, that the forests exist because of suitable rainfall condi- 
tions, and it is fair to assume, unless further evidence is produced, that 
the forests are due to the prevailing rainfall conditions rather than that 
the rainfall is due to the existing forests. .It would seem that in this 
case, cause and effect are somewhat confused in the minds of some ob- 
serves. (See Fig. 91, page 170.) 

89. Rainfall Maps. — The Daily Weather Map of the United States, 
published by the Weather Bureau at Washington, D. C, and also 
issued by a number of the important stations of the Weather Bureau 
shows the barometric pressure, temperature, direction of the wind at 



i See Meteorology, Thomas Russell, p. 86. Forests and Rainfall, H. A. Hazen, 
Monthly Weather Review, 1897, p. 395. The Relation of Forests to Rainfall, 
W. F. Hubbard, Monthly Weather Review, Jan. 1906, p. 24. 



170 



Precipitation. 





Fig. 91. — Distribution of Annual Rainfall and Forests in California (W. F. 
Hubbard, Monthly Weather Review, Jan., 1906). (See page 169). 



Rainfall Maps. 



71 



^.(ijliiilli!i|!J!|!ii 
i M'i'i i fnT! iitri-h — r M 




Fig. 92.— Rainfall Conditions in the United States at 8 A. M., July 16, 1907 

(see page 172). 




Fig. 93.— Rainfall Conditions in the United States at 8 A. M., July 17, 1907 (see 

page 172). 



1 72 Precipitation. 

8:00 A. M., Washington Time, and the precipitation that has occurred 
in the last 24 hours. In the National Weather and Crop Bulletin, 
which is published by the Weather Bureau weekly from April 1 to 
October 1, and monthly for the remainder of the year, maps of the 
weekly and monthly rainfall are also given. Maps of the monthly 
rainfall are also given in the publications of the Monthly Climato- 
logical Data and in the Monthly Weather Review, and rainfall maps 
of annual precipitation, temperature, etc., are published in the Annual 
Summary of Climatological Data, the annual number of the Weather 
Review and the Annual Report of the Chief of the Weather Bureau. 
Occasionally maps are also given in the Weather Review showing the 
data for storms of exceptional magnitude. These publications also give 
the data from which the path of each storm and the resulting precipi- 
tation can be platted. 

For many engineering purposes the annual or even the monthly 
maps of rainfall are only of general value ; a more detailed study 
of the actual occurrence of rainfall is essential and the data should be 
secured and platted in order to bring out the facts necessary to develop 
the information needed. 

go. Occurrence of Precipitation.- — The geographical distribution of 
rainstorms seems largely fortuitous. Individual rainstorms never oc- 
cur twice over exactly the same geographical extent of territory nor 
with equal intensity at any points within the territory covered. They 
are not only irregular in their distribution but progressive in both their 
distribution and intensity, changing from hour to hour during their 
occurrence. The extent of a somewhat general rainstorm in progress 
at 8 :oo A. M. (Washington time) over the Northwest on July 16, 1907, 
is shown by Fig. 92, page 171. On the area over which this storm ex- 
tended, the actual precipitation varied widely and the extent of the 
storm rapidly changed from hour to hour. At 8:00 A. M. on July 17 
the general rainfall had- ceased and the storm had become localized 
as shown by Fig. 93, page 171. The varying character and extent of the 
rainfall as illustrated by those two maps show the extremes of one storm 
which affected the Northwest, and illustrate, in a general way, the ir- 
regularity and lack of uniformity in rainfall occurrence and distribution. 
(See also Fig. 31, page 70). 

It should also be noted that the periodic rainfall maps issued by 
the Weather Bureau for weekly, monthly or annual periods are the 
results of the summation of irregular distribution of numerous rain- 
storms, the irregularities of which can perhaps be more clearly shown 



Occurrence of Precipitation. 



73 





MAY 13 TO MAY 20 



MAY 20 TO MAY 27 





MAY 27 TO JUNE 3 



JUNE 3 TO JUNE tO 





JUNE 10 TO JUNE 17 



JUNE 17 TO JUNE 24 



!NCHES IN DEPTH 



OTO.25 .2S"T0.50 .50T0.75" 75T0 1.' 14, OVER 

Fig. 94. — Distribution of Weekly Rainfall in Wisconsin, 1907 (see 

page 175). 



174 



Precipitation. 









1 

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Rainfall Accompanying Hurricanes. 1 75 

l>y Fig. 94, page 173, which show the weekly distribution of rain- 
fall in Wisconsin for six consecutive weeks in May and June, 1907. 
All such maps are but the result or summation of individual rainstorms 
which occur during the period considered. 

91. Rainfall Accompanying West Indian Hurricanes. — In most 
•cases the rain accompanying the hurricanes from the West Indies falls 



/ - ■ \ V s -—' / J 

/ , ■■ \ \ ^S A. 




/ 


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*^i . —-^ 


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Fig. 96. — Precipitation due to West Indian Hurricane of July 14 to 18, 1916 

(see page 176). 

immediately adjoining the Coast near the point where the storm center 
reaches the land. Occasionally, however, the moisture is carried far 
inland and affects the country at some distance from the Coast. Two 
storms of this kind accompanied by rainfalls of considerable magnitude 
occurred in July, 1916. The first of these two storms entered from the 
Gulf of Mexico through Mississippi about July 5 and was dissipated 
when it encountered the southern span of the Alleghenies in South 
Carolina on July 13. This was followed by a record storm which 



76 



Precipitation. 



reached the coast of South Carolina on July 14, producing a heavy- 
rainfall near the coast on that date, and proceeding to the northwest 
was also dissipated against the Southern Alleghenies on July 16 with 
an unusually intense rainfall. The progress of the storm for the four 
days, July 14, 15, 16 and 17, is shown in Fig. 95, and the combined 
rainfall for the entire storm is indicated on the relief map shown in 
Fig. 96, page 175. These maps show both cyclonic and orographic 
rainfall, resulting from the storm. The rainfall near Altapass North 
Carolina for the 24 hours on July 15 and 16 amounted to 22.22 inches,. 



6S°30 




Fig. 97. — Rainfall on the Island of Porto Rico, resulting from the Hurri- 
cane of Aug. 5 to 9, 1884. 

being one of the heaviest rains which has ever visited the United 
States. 

The rainfall in the island of Porto* Rico accompanying the hurricane 
of August 5-9, 1889, is shown on Fig. 97. Here the source of mois- 
ture is close at hand and the consequent rainfall is much greater than 
would commonly be the case over continental areas. 

g2. Rainfall Accompanying General Cyclonic Storms. — The gen- 
eral distribution of rainfall accompanying the cyclonic storms for 
March 20 to 23, 1913, inclusive has already been shown in Fig. 31, 
page 70, and the distribution for the four following days of March 24 
to 27th, inclusive, is shown in Fig. 134, page 249. These storms led up 
to the extreme flood of March, 19 13, in Indiana, Ohio, and the states 
farther east. 

Figs. 98 and 99. pages 177 and 178, show the summation of the rain 



Rainfall Accompanying Cyclones. 



77 





Hydrology — 12 



78 



Precipitation. 




Rainfall Accompanying Cyclones. 1 79 

accompanying various typical cyclonic storms. 5 Fig. 98, map A, shows 
the path of a cyclone of January 1-16, 191 1, from Arizona on a central 
track with heavy precipitation on both sides of the path, showing the 
influence of moisture from the Great Lakes, the Atlantic and Gulf 
sources and the well watered interior. 

Map B shows the path of the cyclone of April 30-May 5, 1910, of 
Texas origin following a central track. The heavy precipitation is 
to the north of its path and is evidently influenced by moisture from 
the Great Lakes region. 

Map C shows the path of a cycline of March 22-24, 191 1, originating 
in Texas and following the southern track. The heavy precipitation 
is on the south of the path and is evidently from moisture received 
from the Gulf and ocean. 

Map D shows the path of the cyclone of April 19-28, 19 10. There 
are two areas of precipitation separated by a rainless area. The path 
passes between two areas of heavy rainfall and the precipitation is 
evidently derived from the Great Lakes, Atlantic, Gulf and Pacific 
sources of moisture. 

In Fig. 99 map E shows the path of the cyclones of Feb. 22-March 1, 
1910. The northern cyclone caused precipitation from the Pacific 
northwest through the Great Lakes region. The second cyclone on 
the southern track caused the heavy precipitation from the Gulf up 
the Mississippi Valley to the Great Lakes region. 

Map F shows the path of the cyclone of April 16-22, 191 1, which 
entered the United States from Alberta and crossed on a northern 
course. Heavy precipitation followed on both sides of the path, evi- 
dently from the Great Lakes and Atlantic sources, and also to the 
southward, evidently from Gulf sources. 

Map G shows the path of the cyclone of May 23- June 3, 19 10, which 
path was wholly in Canada. The heavy precipitation was much broken 
and was apparently to the south of the path and from Pacific, Atlantic, 
Gulf, Great Lakes and interior sources. 

Map H shows a typical case of the rain accompanying a thunder- 
storm and included in the general rain area of the cyclone of July 
23, 191 1, when the storm center was located over Iowa at 8:00 A. M. 
on July 23, 191 1, Washington time. 

93. Thunder Storms. — Many cyclonic storms are accompanied by 
only slight barometric gradients and the circulation of air is so weak 



5 The Cyclonic Distribution of Rainfall, W. G. Reed. U. S. Weather Re- 
view, Oct. 1911. 



80 



Precipitation. 



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182 



Precipitation. 





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Thunder Storms. 



183 



that smaller local secondary cyclones are frequently generated through 
local conditions. These are usually accompanied by electrical disturb- 
ances and heavy local rainfall and are known as thunder storms. 
Numerous similar local disturbances caused by intense convectional 
action are developed in the equatorial belt where the "afternoon thunder 
storm" is of almost daily occurrence. 

In the United States these storms are of only occasional occurrence 
on the Pacific Coast but increase in number toward the east, and reach 




Fig. 103. 



Jan Feb Mar Apr May June July /lug Sept Oct Nov Dec 

-Average Number of Thunder Storms occurring Monthly at Various 
Stations for the Period 1904-1913, inclusive.s 



a maximum in the extreme southeast. Their normal geographical and 
seasonal occurrence during the ten years 1904-1913 is shown by Figs. 
100-102,° inclusive pages 180, 181 and 182. The normal variation in the 
occurrence of thunder storms, from month to month during the year 
at widely scattered locations is shown in Fig. 103. 

94. Annual Expectancy of Storms. — The expectancy of the annual 
occurrence of thunder storms is shown by Fig. 104 which is based on 
the average for the ten year period 1904- 19 13. 

The approximate mean expectancy for cyclonic storms is illustrated 
by Fig. 105, 7 which is taken from Dunwoody's map summarizing the 



6 Distribution of Thunder Storms in the United States, Wm. H. Alexander, 
Monthly Weather Review, July, 1915. 

7 Bulletin A, U. S. Weather Bureau. 



84 



Precipitation. 




Fig. 104. — Average Annual Number of Thunder Storms in the United States, 
based on observations from 1904 to 1913, inclusive (see page 183). 




Fig. 105. — Annual Cyclonic Storm Frequency in the United States. 



Artifical Production of Rain. 1 85 

international meteorological observations for the period 1878- 1887. 
Later information is contained in Supplement No. 1, U. S. Weather 
Review for 19 14. 

95. Artificial Production of Rain. — Various men have at different 
times declared that they could produce rainfall, usually by one of two 
methods, the discharge of explosives or the liberating of gases. This 
belief obtained such widespread acceptance that the United States 
Government undertook some experimental tests in 1892. Heavy char- 
ges of explosives were sent up into the interior of the clouds by means 
of kites and balloons, and there exploded, but without effect. The 
results obtained by various experimenters have not shown that any 
rain has fallen due to the agency of man. Similarly, the shooting of 
vortex rings, and the ringing of bells, as is done in France at the 
approach of hail storms, have no noticeable effect upon either the 
formation or path of the storm. 

No one who appreciates the great atmospheric movements and 
dynamic changes that take place during rainstorms will believe that, 
by any process possible to man, any material control can be effected 
over such storm movements. 

LITERATURE 

CAUSES OF RAINFALL 

The Cause of Rain and the Structure of the Atmosphere, Franz A. Velschow. 
Trans. Am. Soc C, E. Vol. 23, 1890, p. 303. 

The Causes of Rainfall, Prof. W. M. Davis. Journal New England Water 
Works Association. June 1901. 

How Rain is Formed, H. F. Blanford. Sci. Am. Sup. May 11, 1889. 

Analysis of the Causes of Rainfall, G. E. Curtis. Bui. No. 7, Forestry Di- 
vision U. S. Dept. Agriculture, 1893, p. 187. 

CONDITIONS AFFECTING RAINFALL 

Effect of Wind Currents on Rainfall, Curtis. Eng. News, Jan. 3, 1885. 
Mountain and Lower Level Differences. Rep. Chf. of Engrs. U. S. Army. 

1874, part II, p. 375. 
Irrigation and Increase of Rainfall. Eng. News, 1906, part I, p. 213. 
Forests and Rainfall, H. A. Hazen. Eng. News, 1898, part I, p. 5. 
The Relation of the Atlantic Plain to the Humidity of the Central States and 

Plateau Region, Science, July 18, 1913. 

INFLUENCE OF FORESTS 

Relations of Forests to Rainfall and Runoff. Eng. News, 1908, part II, p. 365. 
Effect of Forests on Rainfall, W. L. Moore and G. F. Swain. Eng. News, 

1910, part I, p. 246 and p. 427. 
Effect of Forests on Snow and their ComMned Effect on Water Supply. Eng. 

News. 1901, part II, p. 209. 



86 Precipitation. 



Effects of Forests on Rainfall. Rep. Ch. of Engrs. U. S. Army. Eng. News, 
1875, part II, p. 172; 1879, p. 1211; 1884, p. 662. 

Forest Influences on Rainfall and Climate, B. E. Fernow, M. W. Harrington, 
Cleveland Abbe and G. E. Curtis. Bui. No. 7, Forestry Div., U. S. Dept. 
Agriculture, 1893. 

Pseudo Science in Meteorology, B. E. Fernow. A warning against conclu- 
sions as to effects of forests on meteorological conditions and stream 
flow. Science, May 8, 1896. 

RAIN MAKING 

The Facts about RainmaJcing, G. E. Curtis. Eng. Mag. July, 1892. 

Rainmaking, Prof. Fernando Sanford. Sci. Am. Sup. Aug. 11, 1894. 

Chicago, Rock Island and Pacific Railway Experiments. Eng. News, 1895, 
part I, p. 105. Eng. News, 1901, part I, p. 32. 

Dept. of Agriculture Circular Letter. Eng. News, 1894, part I, p. 318. Dis- 
couraging farmers in hope of rain production. 

Production of Rain by Concussion- Eng. News, 1891, part II, p. 34-307. 

Experiments in Australia. Eng. News, 1903, part II, p. 364. 



CHAPTER VIII 



RAINFALL MEASUREMENTS AND RECORDS 

96. The Measurement of Precipitation, Instruments Used. — 

The ordinary rain gage as used by the United States Weather Bureau 
(Fig. 106,) consists of a galvanized iron cylindrical can, eight inches 
in diameter, the mouth of which is circular, beveled on the outside to 



Front View 



Vertical Section 






Horizontal Section, E.F 




I ? 3. 4 S b 7 3 9 IO II 12 13 



IS 20 21 2Z23 24 



Sca/e in inches 
Fig. 10G. — The Ordinary Form of Rain Gage 

form a sharp edge. This receiver is funnel-shaped ; the orifice leading 
from the funnel discharges into a brass cylindrical vessel, twenty inches 
in depth, the inside area of which is exactly one-tenth of the area of 
the receiver rim. 

The depth of rain caught in this interior tube is measured by means 
of a wooden scale to tenths of an inch, thus measuring the rainfall 
caught in the gasre to hundredths of an inch. 



1 88 Rainfall Measurements and Records. 

When used in measuring snowfall, the funnel-shaped entrance or 
rim of the tube is removed and the snow is caught directly in the 
outer can. The snow is then melted and the equivalent depth of 
water measured as in the case of rainfall A more satisfactory means 
of obtaining the amount of precipitation occurring in the snowfall is, 
however, to take several samples by inverting the can of the gage 
over a field of snow free from drifting or other wind effects, and 
melting the samples so taken. 

Recording gages for measuring the quantity and rate of precipita- 
tion operate on various principles. The one perhaps in most general 
use in this country is the tipping-bucket gage. This gage is usually 
so constructed that a bucket becomes filled with i/ioo inch of rainfall, 
when it tips, brings another bucket into position, and records the 
movement upon a revolving drum. 

"The collector, and, in some gages, the middle section, are sep- 
arately detachable from the lower section of the inclosing case, in 
order to facilitate access to all the parts. 

"The top section, called the receiver or collector, is made of a sharp- 
edged brass rim, accurately twelve inches in diameter inside, and pro- 
vided with a funnel-shaped bottom and a small tube at the center 
so that all the water falling within the collector is conducted to a 
point directly over the center of the tipping-bucket bearings. The 
middle section is made of galvanized iron, with a hinged door, and 
the lower section, or reservoir, is also of galvanized iron, and pro- 
vided with a brass stopcock at the bottom, for emptying the gage of 
water. 

"A portion of the bucket frame and the tipping bucket is mounted 
on a detachable brass frame carried on brackets within the inclosing 
case. The brass bucket is divided by a central partition into two 
equal compartments. 

"This bucket is mounted on suitable bearings placed below the cen- 
ter of gravity. Two stop pins on the side of the bucket limit the move- 
ment of the bucket on its axis and permit it to rest in one of two posi- 
tions, in which either one or the other of the compartments of the 
bucket is presented in such a manner that it will receive and retain the 
water delivered through the funnel to the collector. The weight of the 
bucket and the position of its center of gravity have been so adjusted 
in relation to its supports that when one of the compartments has been 
charged with the quantity of water representing one one-hundredth of 



Measurement of Precipitation. 1 89 

an inch of rain in the twelve-inch gage, the bucket tips over upon its 
bearings, emptying the water from the one compartment, and at the 
same moment presenting the other compartment to receive the incom- 
ing water. The water thus delivered from the buckets is retained in 
the reservoir section for subsequent measurement in bulk. 

"The automatic registration of each hundredth of an inch of rain- 
fall, that is, each tip of the bucket, is effected by aid of an electrical 
circuit closer. A short sector is attached to the tipping bucket and 
when the bucket is at rest in either of its limiting positions the sector 
stands near to, but not in contact with, a pin on an insulated contact 
spring. 

"In the act of tipping, after the bucket has moved a little, the sector 
makes contact with the pin, and rubs over it during the greater part 
of the subsequent motion. This effectually closes the electric circuit 
which is formed between the whole metallic framework, including the 
bucket, and the insulated spring. During the last portion of the tip of 
the bucket the sector slips off and moves a small distance away from 
the pin, thus opening the electric circuit, and also leaving the bucket 
perfectly free to tip with the next hundredth of an inch of rain." 1 ' 

Other recording gages operate by floats or by weighing. In the 
case of the float type of gage, a float rises and falls with the increase 
and decrease of the water level within the receptacle and by so doing 
traces a line upon a revolving drum. In the Marvin weighing rain 
gage, the necessary vessel is kept in balance as the rain descends, by 
a counter-weight which is automatically moved by a magnet. Each 
impulse which is recorded on the sheet attached to the revolving drum, 
corresponds to i/iooo of an inch of rainfall. 

97. Exposure of Rain Gages. — The exposure of rain gages is a 
very important matter if accurate results are to be attained. The 
wind is the most serious disturbing cause, and when it blows against 
the gage it forms eddies near and above the mouth of the gage and 
frequently carries away the precipitation, especially when in the form 
of fine rain or snow and hence causes the gage to give erroneous re- 
sults. Snow is frequently blown from the gage even after it has 
fallen into it, and the ordinary gage is of little value for the measure- 
ment of snowfall. 

The stronger the wind the more it is apt to affect the catching of 



1 Measurement of Precipitation, C. F. Marvin. Circular E. Instrument Di- 
vision, U S. Weather Bureau. 



1 90 Rainfall Measurements and Records. 

precipitation, and two gages differently exposed are apt to register 
considerable differences even when located quite near each other. 

"In a high location eddies of wind produced by walls of buildings 
divert rain that would otherwise fall in the gage. A gage near the 
edge of the roof, on the windward side of a building, shows less rain- 
fall than one in the center of the roof. The vertical ascending cur- 
rent along the side of the wall extends slightly above the level of the 
roof, and part of the rain is carried away from the gage. In the 
center of a large, flat roof, at least sixty feet square, the rainfall col- 
lected by a gage does not differ materially from what is collected at 
the level of the ground. A gage on a plain with a tight board fence 
three feet high around it at a distance of three feet will collect six 
per cent more rain than without the fence. These differences are due 
entirely to wind currents. 

"The rain gage should, if possible, be located in an open space un- 
obstructed by trees, buildings or fences. Low bushes and fences, 
or walls that break the force of the wind in the vicinity of the gage 
are, however, beneficial, if at a distance not less than the height of the 
object. Gages should be exposed upon roofs of buildings only when 
better exposures are not available ; and, when so located, the mid- 
dle portion of a flat, unobstructed roof, generally gives the best re- 
sults." 2 

98. Location of Rain Gages of the United States Weather 
Bureau. — The gages at the United States Weather Bureau stations 
in large cities are usually located on flat roofs. This altitude, together 
with the influence of surrounding buildings, has a considerable effect 
upon the air currents around the gage, and consequently the propor- 
tion of actual precipitation caught by the gage is more or less affected. 

Alfred J. Henry 3 gives the following comparisons in rain gage 
registers on buildings and in the open areas : 

St. Louis — The rain gage is located on the city post office, twenty feet 
from the edge of the roof and 100 feet above the street. The Forest 
Park rain gage is situated four miles west, in an open space seventy- 
five feet from any object and with its rim four feet above the ground. 

A comparison of the records for five years (1891-1895) shows that 
the post office gage records greater precipitation in the winter, while 
the Park gage shows the greater amount in warm weather, especially 



2 Ibid. 

3 Rainfall of the United States, A. J. Henry. Report of the Chief of the 
Weather Bureau, 1896-7. 



Effect of Wind. 191 

in May and June. On the yearly average, the park gage records a 
rainfall of about two inches — or five per cent greater than the post 
•office gage. 

Philadelphia — The Weather Bureau gage is located on the post 
office, 1 66 feet above the street. Mr. L. M. Dey made a comparison 
between the post office gage and a ground gage located three miles 
east. An average covering six years shows that the ground gage 
registered three inches or eight per cent per year more than the post 
office gage. 

New York — Weather Bureau gage is situated on the roof of a 
building 150 feet above the street. A comparison is made with the 
records of the Central Park gage, which is sixty-three feet above the 
ground. Covering a period of twenty years, shows that the Weather 
Bureau gage registers 2.17 inches or about 5 per cent greater than the 
•Central Park gage. 

These variations are probably due to the effect of local air currents 
in carrying a greater or less amount of the falling rain out of the mouth 
of the gage. 

99. The Effect of Wind.— The value of rainfall records for 
hydrological, agricultural or meteorological studies depends upon the 
accuracy with which they represent the actual occurrence of rainfall 
over the area under investigation. Any single gage can measure only 
the precipitation occurring within its own areas, and its application to 
a wider area must be on the assumption that the precipitation is uni- 
form over the area to which the data are applied or that the rainfall 
varies uniformly between gages when the data from two or more gages 
.are utilized. 

It is well understood that local topography and the position of the 
gage with reference to the height above the surface of the ground and 
with further reference to trees, buildings or other objects, together 
with the relative direction and amount of the wind, may produce great 
differences in the amount of rainfall collected by a series of gages. 

The difference in the amount of rainfall which will be collected by 
gages exposed at different heights above the surface of the ground has 
been conclusively shown to be due to wind currents. Jerome explained 
this phenomena as follows : 4 

"To show clearly the nature of this effect we may imagine the stream 
•of air M N (Fig. 107, page 192) to be suddenly contracted at B C to 



4 See Philosophical Magazine, 1861; also The Effects of Wind Currents on 
Rainfall. G. E. Curtis, Signal Service Notes, No. 16, 1884. 



92 



Rainfall Measurements and Records. 



half its previous thickness, so that of course, it must there commence to 
move with double velocity. At A D the stream dilates to its original 
size, and of course recovers its first velocity. The course of equidistant 
rain drops falling into wind under such imaginary circumstances would 
be represented by the oblique lines, and it is obvious that less rain would, 
fall in the windward part of the contracted space than elsewhere." 




Fig. 107. — Effect of Wind upon the Catchment of the Rain Gage (See 

page 191). 

For the same reason, with rain gages located on a roof the gages to> 
the leeward will catch more rain than those to the windward, and 
with the location of gages on a mountain top or in other positions 
where the direction or intensity of the wind may seriously affect the 
catchment of the rain, considerable difference will be found between, 
gages set in the same vicinity. 4 

The difference in the measurement of rainfall by various gages is 
often marked. In the winter of 1852-3 there was established at Roth- 
amstead Experimental Station, in England, a rectangular rain gage 
6 feet wide by 7 feet 3.12 inches in length, having an area of one-thou- 
sandth of an acre. 5 This large gage was established partially for the 



5 Amount and Composition of Rain and Drainage Waters Collected at Roth- 
amstead, by Lawes, Gilbert & Warington, Jour. Royal Agric. Soc. of England. 
Vol. 17, 1881, p. 224. 



Effect of Wind. 193 

accurate determination of rainfall and partially to allow the collection 
of the rain in sufficient quantities for chemical analysis. The surface 
of the gage was two feet above the level of the surrounding ground. 
Closely adjoining this gage and at the same elevation above the ground 
surface was placed an ordinary rain gage consisting of circular copper 
funnel 5 inches in diameter, delivering into receptacle enclosed in a 
metallic cylinder. Observations for 28 years showed that the small 
gage indicated a distinctly less average quantity of rainfall than the 
larger gage. The means of the 28 years readings (1853-80) of both 
the large and small gages are shown in Table 14. 

TABLE 14. 

Comparison of the Large and Small Rain Gages. 
(Means of 28 Years) 

Mean Monthly Rainfall D efficiency of Small Gage 

Large Gage Small Gage Actual Percent 

Inches Inches Inches 

January 2.500 2.263 0.327 12.6 

February 1.72S 1.508 0.220 12.7 

March 1.693 1.399 0.294 17.4 

April 2.008 1.803 0.205 10.2 

May 2.329 2.149 0.180 7.7. 

June 2.451 2.272 0.179 7.3 

July 2.704 2.533 0.171 6.3 

August 2.643 2.440 0.203 7.7 

September 2.638 2.403 0.235 8.9 

October 3.089 2.784 0.305 9.9 

November 2.345 2.113 0.232 9.9 

December 2.084 1.861 0.223 10.7 

Total for Year 28.302 25.528 2.774 9.8 

Some of the causes contributing to this difference were manifest, for 
example: a heavy snowfall was much better retained by the large gage 
than by the small one ; the deposits of mist, dew and frost were also dis- 
tinctly greater with the large gage. The effect of winds on the smaller 
gage was probably the main contributing factor for other differences. 

ioo. Records of Rainfall of the United States. — The sources of 
rainfall data in the United States, so far as generally available, may be 
found in the following publications : 

Abstracts of all the records of observations of rainfall which have 
been made from the early settlement of the country down to the close 
of the year 1866, so far as they could be obtained, were contained in 
Smithsonian Contribution to Knowledge No. 222, published in 1874, 
and entitled "Table and Result of the Precipitation and Snow in the 
United States," by C. A. Schott. 
Hydrology — 13 



1 94 Rainfall Measurements and Records. 

In 1872, the United States Signal Service began the publication of 
the results of the observations made at various army stations by the post 
surgeons of the United States Army in the "Monthly Weather Review," 
including in this publication various reports of the State Weather 
Services and voluntary observers, Canadian stations, and various 
stations maintained by the Central Pacific Railway Company, the 
Hydrologic office, Navy Department, and the New York Herald 
Weather Service. 

Upon the establishment of the U. S. Department of Agriculture in 
1 89 1, the Weather Bureau was organized as a branch of this service, 
and the Weather Review has since been published by this Bureau. 
In general this Review has summarized the current data received 
from both land stations and ocean vessels, as well as from several Euro- 
pean and Asiatic stations, but did not include the daily rainfall observa- 
tions until July, 1909, when it was enlarged to embody the daily observa- 
tions at each of the weather stations, including also various additional 
data secured by an association with various other bureaus of the govern- 
ment whereby the latter assisted in the collection of data not hitherto 
available from the various other localities. This continued until Jan- 
uary, 1914, when the publication of rainfall data was dropped from 
the Review. 

From the early '90's to 1909, the climate and crop service of many 
of the states published each month in various forms the rainfall and 
other climatological data for the particular state. In 1909, the state 
work was largely discontinued on account of the publication of this 
work in the Weather Review. 

The state climate and crop service reports were issued in small edi- 
tions, sometimes the early report being published only in a newspaper 
at the Section Center. They are not generally available, although 
usually complete files are found at the office of the Weather Bureau 
Section Center where duplicates for some special months and years 
may occasionally be obtained. These reports, more or less complete, 
can usually be found at the principal offices of the United States 
Weather Bureau. 

Since January, 1914, the Weather Bureau has published, under the 
head of "Climatological Data," the daily rainfall data of various sec- 
tions. These sections follow in general the geographic division of 
the states ; the exceptions are that the Maryland section includes Dela- 
ware and the District of Columbia, and the New England section com- 
prises the New England States. These reports are printed at the sev- 



Records in United States. 195 

eral Section Centers and are generally available to those interested in 
the local sections. A limited edition, including all the various sections, 
is assembled and bound at the Washington office for Service use and 
exchange. 

The Weather Bureau has also published a summary of the monthly 
rainfall data for the United States in 106 sections. This summary is a 
combination of all the available rainfall data since 1870 when the gen- 
eral Meteorological Service of the United States was first established. 
Most of these sections are brought up to include the year 1908, while 
others, published later, include the year 1909. The summary is bound 
in two volumes, known as Bulletin W. 

The report of the Chief of the United States Weather Bureau, from 
the year 1891 to date, includes the annual and monthly rainfall rec- 
ords and other climatological data. 

101. Dependability of Precipitation Records. — The dependability 
of many ancient rainfall records, taken in unknown ways and under 
unknown conditions, are open to serious question. From that which 
has been previously stated, it is obvious that many of the present rec- 
ords are also subject to more or less error. Subject, as they are, to 
considerable variations, it would seem unwise to use great refinement 
in the calculations of rainfall, and in recording rainfall one decimal 
place is probably the ultimate limit of possible accuracy. It should also 
be recognized that the rainfall maps, showing lines or belts of equal rain- 
fall, are only approximately correct, and that it would be impossible to 
show by such lines small differences in annual rainfall of less than two 
or three inches. 

When considering the occurrence of rainfall in particular storms, the 
conditions are further complicated by the fact that not all the stations re- 
porting furnish data taken at the same time. Most of the stations read 
the accumulated daily precipitation at 8 P. M., Washington time. The 
principal Weather Bureau Stations record the rainfall that occurs 
from midnight to midnight, while at a number of river stations the 
rainfall is recorded at 8 A. M. The consequence is that a rainstorm 
which occurs at essentially the same time at two different stations is 
frequently recorded as occurring on different days. 

Most of the principal Weather Bureau Stations are located in cities, 
and observations are made on top of high buildings where air cur- 
rents, frequently greatly modified and controlled by other buildings in 
the immediate vicinity, seriously affect the measured rainfall. It is 
probably true that the rainfall records from few of the principal sta- 



! 96 Rainfall Measurements and Records. 

tions in the United States fairly represent the local rainfall within 
several per cent. Not only is the record of rainfall probably inac- 
curate, but the conditions from year to year are apt to change through 
changes both in the construction or arrangement of surrounding 
buildings and in the changes made necessary by the changes in loca- 
tion of the Weather Bureau offices. For example, the Chicago office 
of the Weather Bureau occupied the Major Block (elevation ninety- 
three feet) from June 8, 1873 to December 31, 1886; the Chicago 
Opera House building (elevation 132 feet) from Jan. 1, 1887, to Jan.. 
31, 1890; the Auditorium Tower (elevation 238 feet) from Feb. 1, 
1891, to June 30, 1905, and the Federal building (elevation 133 feet) 
from July 1, 1905, to date. The exposure of the rain gages at these 
various locations leads to the conclusion that the records are not strictly 
comparative, but are modified by the influence of the local condition. 6 

It is evident that, as many rainstorms have definite limits and do 
not shade off gradually to nothing, as is shown by the clear lines of 
demarcation sometimes left in the dust by passing showers, there may 
be considerable legitimate difference in the readings of rain gages 
which are placed close together, in addition to such differences as 
may be due to the wind. Hellmann found that monthly totals of 
gages only 1,500 feet apart would differ by five per cent, while for 
individual storms they might differ even 100 per cent., and considerable 
difference in the annual rainfall must be expected in gages even five 
miles apart. 7 The above may account to some extent for the differ- 
ences noted in the gages at St. Louis, Philadelphia and New York, 
mentioned in Sec. 98. The matter of securing correct rainfall records 
has not received the attention that its importance demands, and it is 
to be hoped that the U. S. Weather Bureau, which is doing such valu- 
able service in many ways, will give more attention to this matter 
which is of great importance in hydrological investigations. 

102. Estimating Rainfall on any Area. — From the previous dis- 
cussion it is evident that in estimating the amount of rain which has 
fallen on a given drainage area during a given period, much doubt will 
exist as to the accuracy of the results which may be obtained. Rainfall 
stations are often widely separated and undoubtedly their records do not 
always fairly represent the rain falling on intervening territory (see 
Sec. 121, page 245 and the records of Weather Bureau Stations) for 



e The Weather and Climate of Chicago, H. J. Cox and J. Armington Bul- 
letin No. 4, Geographical Society of Chicago, p. 152. 
7 Descriptive Meteorology, W. L. Moore, p. 209. 



Estimating Rainfall. 



97 



J.9loLima 




Fig. 108.— Rainfall of March 23-27, 1913, in the Miami Valley. 



1 98 Rainfall Measurements and Records. 

single storms or for .short periods are at the best only roughly approxi- 
mate as to the rain falling on the area between stations, and approxi- 
mate for the annual rainfalls. As the number of stations increases on 
and closely adjoining a drainage area, the accuracy of the average rec- 
ords as representing the average rainfall on the intervening area will in- 
crease, provided the stations are fairly well distributed. In making- 
such estimates the records of rainfall stations bunched on the area 
should be segregated and averaged and given only such weight as will 
represent a fairly uniform distribution of stations compared with the 
stations on the remaining area. The most accurate results can usually 
be obtained by drawing isohyetal lines on the rainfall map, determining 
the area of a given density of rainfall by means of a planimeter, and 
then calculating the total as the weighted average of areas with given 
densities of rainfall. For example, in the rainfall of March 23-27, 
1913, on the Miami River drainage area (Fig. 108, p. 197), the average 
of the rainfall at all stations (omitting Lima, Salamonia and Camp 
Dennison) is 9.01 inches, while the weighted average based on the area 
between the isohyetal lines is 9.5 inches. In this case the stations are 
fairly well distributed. In many cases the distribution of stations 
would be much more unsatisfactory and the error in the estimate much 
greater. 

LITERATURE 

MEASUREMENTS OF PRECIPITATION 

Rain Gages 

Measurement of Precipitation, C. F. Marvin. U. S. Weather Bureau Circu- 
lar E, Instrument Division. 

The Practical Value of Self-recording Ram Gages, E. B. Weston. Engineer- 
ing News, 1889, Vol. 21, p. 399. 

Self-Registering Rain Gages and their Use for Recording Excessive Rainfalls. 
Eng. Rec. 1891, Vol. 23, p. 74. 

Self Registering Rain Gages, John E. Codman. Eng. Rec, March 14, 1890. 

Self Registering Rain Gages and Their Use for Recording Excessive Rain- 
fall, Rudolph Hering. Eng. Rec. Jan. 3, 1891. 

Rain Gage Used at Philadelphia for Rainfall Measurements. Eng. Rec. Nov. 
5, 1892. 

Dalton's Rain Gage, Rev. J. C. Clutterbi;ck. Proc. Inst, of C. E., Vol. 60, 
1880, p. 157. Prof D. T. Ansted. Proc. Inst. C. E., Vol. 50, 1877, p. 96. 

Rain Gages vs. Dickinson's Gage, S. C. Homersham. Proc. Inst. C. E., Vol. 
14, 1855, p. 81. 

Rain Gage, C. Greaves. Proc. Inst. C. E., Vol. 18, 1859, p. 391. 

Observations with Staff Gages, S. C. Homersham. Proc. Inst. C. E., Vol. 7, 
1848, p. 276. 



Literature. 1 99 

Description of Rain Gage with Evapometer for Remote and Secluded Sta- 
tions, H. F. Blanford. Proc. Inst. C. E., Vol. 66, 1881, p. 398. 

Self Registering Rain Gage, A. Frank. Proc. Inst. C. E., Vol. 77, 1884, p. 414. 

Ferguson Automatic Rain Gage. In use at Worcester, Mass. sewage purifica- 
tion works. Eng. News, 1900. Part II, p. 448. 

Rainfall of the United States, A. J. Henry. Rept. of Chief of Weath. Bureau, 
1896-7. 

The Amount and Composition of Rain Waters at Rothamstead, Lawes, Gilbert 
and Warington, Jour. Agric. Soc. of England, Vol. 17, 1881. See also 
Proc. Inst. C. E., Vol. 20, 1860, Vol. 45, 1876 and Vol. 105, 1891. 

EFFECTS OF WIND OX RAINFALL MEASUREMENT 

Does the Wind Cause the Diminished Amount of Rain Collected in Elevated 
Rain Gages? Desmond Fitzgerald. Jour. Asso. of Eng. Soc, 1884. 

The Effect of Wind-Currents on Rainfall, G. E. Curtis. Signal Service 
Notes No. 16, 1884. 

Determination of the True Amount of Precipitation, Cleveland Abbe. Ap- 
pendix I, Bulletin No. 7, Forestry Division, U. S. Dept. Agriculture, 1893. 

The Rain Gage and the Wind, Month. Weath. Rev., Oct. 1899, p. 464. 



CHAPTER IX 

ANNUAL RAINFALL IN THE UNITED STATES AND ITS 

VARIATION 

103. Quantity and Distribution of Average Annual Rainfall. — 

The quantity of the average annual rainfall in the United States 
varies greatly at different points, as will be seen from Fig. 109, page 
201, which shows the distribution of the average annual rainfall based 
on average local rainfalls to June 1, 1916. From this map it will be 
noted that "from the great plains westward the lines of equal rainfall 
are, approximately, north and south. In the Southern States, east of 
Texas, they are approximately parallel to the Gulf coast. In the East- 
ern States they are approximately parallel to the Atlantic coast. In 
the Lake region, while they approach parallelism to the parallels of 
latitude, yet there are some variations, evidently due to the effects of 
these great bodies of fresh water and their temperature at different 
seasons of the year. In the vicinity of Cape Hatteras and on the 
Peninsula of Florida, other influences come into play, modifying the 
direction of the lines of equal rainfall. Cape Hatteras is the point of 
highest rainfall along the Atlantic coast, due, undoubtedly, to the sea- 
sonal winds which pass at sea and reach, more or less, this prominent 
point. On the Peninsula of Florida we approach the tropical region 
and approximate the laws of tropical rainfall. East of the ninety-fifth 
meridian the rainfall decreases as the latitude increases. West of that 
in general the lines run north and south." x 

It may be observed that the rainfall apparently decreases with in- 
crease in elevation : This is very noticeable in passing along, for in- 
stance, the parallel of latitude 40 . The annual rainfall on the coast 
of New Jersey ranges from 40 to 50 inches. As we pass westward 
we come to the area where the rainfall is about 40 inches. This rain- 
fall continues along the parallel until the vicinity of the Mississippi 
River is reached, when it decreases with the comparatively rapid 
ascent of the slope to the great plains. By the time Kansas is reached 
the annual rainfall has fallen to 30 inches ; in western Kansas it is only 
20 inches, and in passing the boundary of western Kansas we pass 
the annual rainfall line of 15 inches. 



1 Bulletin C, Weather Bureau, page 13. 



Quantity and Distribution. 



20 




202 Annual Rainfall in the United States. 

These conditions of rainfall are, however, undoubtedly due to dis- 
tance from sources of vapor origin instead of to altitude, which, as 
shown in another place, with other things being equal, increases the 
rainfall rather than diminishes it. 

In general therefore, the distribution of the mean anuual rainfall is 
explainable on the basis of the factors already discussed. Among the 
mountains, on the Pacific Coast and in the great interior basin the 
phenomena of precipitation are more complex and the reasons for differ- 
ences in distribution not so evident, on account of topographical irregu- 
larities. 

Even in portions of the country where the topographical relief is ap- 
parently not sufficient to modify the quantity of rainfall, considerable 
differences sometimes occur within short distances for which there 
seems no adequate explanation. For example, Mather and Meadow Val- 
ley, Wisconsin, are about 6.5 miles apart but the rainfall of Mather ex- 
ceeds that at Meadow Valley by about 4 inches per year, which is fairly 
uniform for the six years of parallel records : 

Year 1912 1913 1914 1915 1916 1917 Mean 

Mather 33.45 37.43 32.38 31.51 32.39 30.64 32.96 

Meadow Valley 30.27 30.79 27.77 31.49 27.46 25.59 28.89 

Difference 3.18 6.64 4.61 .02 4.93 5.05 4.07 

Appleton and Menasha, Wisconsin, are located about 7 miles apart 
but there is a mean difference in the annual rainfall at these two stations 
of about 3.4 inches, the Appleton rainfall averaging higher. Here, how- 
ever, the differences are not constant as will be noted from the parallel 
records for the last eight years : 

Year 1910 1911 1912 1913 1914 1915 1916 1917 Mean 

Appleton 24.43 36.65 30.54 37.08 35.82 28.97 33.95 28.00 31.93 

Menasha 23.45 32.30 31.55 29.66 30.29 29.11 28.74 25.09 21.57 

Difference 98 4.35 —1.01 7.42 5.53 —.14 5.21 2.91 3.36 

It is readily understood that extreme storms will frequently give rise 
to great differences in rainfall at stations closely adjoining, but fortuit- 
ous circumstances will seldom tend toward one direction for any con- 
siderable term of years, and when such tendency is displayed it would 
seem to indicate some constant influence which affects the phenomena 
in the direction noted. 

104. Variation in Annual Precipitation. — While the causes that 
produce the normal local rainfall are difficult to determine, the causes 
which produce the variations that occur in the total annual precipita- 
tion and in its distribution are still more difficult to trace. The in- 



Variation in Annual Precipitation. 203 

vestigator must confine himself largely to a study of the actual varia- 
tion and the actual distribution in endeavoring to determine their lim- 
its and the effects due to them. The map of average annual rainfall 
is of value for only a general view of the subject. Even the study of 
the general rainfall map from year to year gives only limited informa- 
tion (see Figs, no and in, page 204) ; although the variations in such 
maps begin to show the large departures from average conditions 
that occur locally. The average or mean conditions of precipitation 
are of only general importance. The extreme conditions are those 
most directly modifying runoff and which seriously affect hydraulic 
problems. A water supply, for whatever purpose, should be constant 
in quantity or vary only as the demand for water varies , otherwise 
continuous service will be interrupted or must depend on other pro- 
visions ; hence the occurrence of minimum conditions will largely modify 
the nature and extent of works intended to conserve and equalize such 
supplies. The maximum precipitation resulting in extreme flood flows 
must, on the other hand, modify works intended for escapement and 
flood protection. 

The two maps of annual rainfall show a considerable variation in 
the rainfall for the years 1906 and 1904. They show, however, a 
general similarity in distribution even while great local differences are 
discernable. As a general rule it is found that great variations in 
rainfall are more or less local in character, and while it may be very 
dry in one part of the United States, it is apt to be unusually wet in 
some other portions. In general, wet and dry periods may occur in 
areas of considerable magnitude, but the great differences are more 
readily discernable when smaller areas are compared. 

105. Variation in Annual Rainfall in Limited Areas. — For special 
purposes, a detail study of the local variations from the average con- 
ditions is necessary. Great variations take place in the annual rain- 
fall of every locality. Sometimes the annual rainfall will be consider- 
ably below the average for a series of years, and then for a number 
of years the average may be considerably exceeded. No general law 
seems to hold, however, in regard to this distribution and the variation 
seems to occur either without law or by reason of laws so complicated 
as to defy determination. The variations in the distribution of the 
annual rainfall in the State of Wisconsin for 24 years are shown 
by Figs. 112 and 113, pages 205 and 206. From these maps it can 
clearly be seen how greatly the distribution of rainfall throughout the 



204 



Annual Rainfall in the United States. 




Fig. 110.— Annual Rainfall 1906. 




Fig. 111.— Annual Rainfall 1904. 



state differs in different years from the average annual rainfall as shown 
by Fig. 114. Even in the State of Wisconsin there are few, if any, 
years when the rainfall in the entire state is uniformly very high or very 



Variation in Annual Precipitation. 



205 




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206 



Annual Rainfall in the United States. 




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Fig. 113. — Annual Rainfall in Wisconsin (see page 204). 



Variation in Annual Precipitation. 



207 



low. The year 1910 (Fig. 113) was perhaps the year of lowest average 
rainfall, and the year 1903 (Fig. 112) the year of highest average rain- 
fall. Fig 114 indicates that on the average the rainfall is fairly well 



89' 



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47 



46° 




Fig. 114. — Mean Annual Rainfall in Wisconsin, 1895-1918. 

distributed and gives no indication of the great variations that actually 
obtain over areas of considerable size, as indicated by the maps of 
Figs. 112 and 113. Even these maps fail to indicate the great range of 
variation that takes place in more limited localities. 

106. Variation in Local Annual Rainfall. — The variation in an- 
nual rainfall at various selected stations in the United States is shown 
in Figs. 115 and 116, pages 209 and 210, on which are also indicated 



208 Annual Rainfall in the United States. 

the means for each station. From this diagram the annual variation 
and the relation of such variation to the mean are clearly shown. 

Some idea of the limiting conditions, and the average relations of 
extremely dry and extremely wet periods can also be determined from 
this diagram. 

The question is frequently raised as to whether or not the total an- 
nual rainfall is increasing or decreasing, and many believe that the 
removal of forests has a detrimental effect and that the cultivation of 
ground, and especially irrigation, has increased the annual rainfall. 
Meteorologists are generally of the opinion that the causes which in- 
fluence rainfall are too great and too far-reaching to be modified by 
any possible works of man, and the records seem to bear out this 
opinion. 

In the investigation of the tendencies of annual rainfall or other 
similar varying phenomena to follow harmonic laws, the tendencies may 
frequently be studied to advantage by platting the means for five or 
ten-year periods or the progressive means calculated by one of the usual 
formulas. By any of these methods erratic occurrences are eliminated 
and any gradual change is more clearly' developed. 

In Figs. 117 and 118, pages 211 and 213 the progressive means have 
been calculated by the formula 

a + 4b + 6c + 4d + e 



16 
in which a, b, c, d, and e are the annual rainfall for successive years and 
c' is the progressive mean for the middle year in which the actual rain- 
fall was c. In Fig. 117 each locality was represented by the average of 
two or more stations, and to these averages the above method was ap- 
plied. The figure shows the progressive mean of the rainfall in 
various sections, of the United States for a considerable period of 
years, and illustrates the fact that in every section the rainfall is 
subject to considerable variations. From this diagram it is easily 
seen that if the rainfall record .for only a limited series of years is 
considered, conclusions might readily be drawn from almost every 
section that the rainfall is increasing or decreasing, according to the 
data selected. For example, from the diagram of the rainfall of New 
England, a continued increase is noted for the year 1838, when the 
progressive mean was 8.8 inches below the mean for the period, to the 
year 1890 when the progressive mean was 7.5 inches above the mean 
for the period ; while from 1890 to 1907 there is a continued decrease 



Variation in Annual Rainfall. 



209 



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Fig. 115. — Variation in Annual Rainfall at Various Stations (see page 207). 

Hydrology — 14 



210 



Annual Rainfall in the United States. 



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Fig. 116. — Variation in Annual Rainfall at Various Stations (see page 207). 











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Variation in Annual Rainfall. 



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Fig. 117. — Rainfall, Progressive Means (see page 208). 



in the progressive mean of over ten inches. In Wisconsin, from the 
year 1840 to 1881, an increase of 13.5 inches in the progressive mean 
is shown, while the years 1881 to 1902 show a decrease of 12 inches. 
It is evident therefore, that to demonstrate either an actual increase or 
decrease in the mean annual rainfall, records are required for a much 
longer period than is available in the United States or elsewhere. 

The long periods during which the progressive mean is sometimes 
below or above the mean for the period should also be noted. For 



2 1 2 Annual Rainfall in the United States. 

example, in New England the progressive mean was below the mean 
for the period for twenty-six years from 1833 to 1859, and above for 
the twenty-three years from 1859 to 1882. In Wisconsin, the pro- 
gressive mean was above the period mean for twenty years from 1867 
to 1887, and below the mean for the ten years from 1892 to 1902. 
Usually, however, the departure in one direction is for more limited 
periods, as an examination of the various curves will show. The 
error* that must therefore occur in drawing any conclusions from a 
short series of observations is manifest. 

These diagrams of mean rainfall, together with much longer rec- 
ords in foreign countries, lead to the conclusion that while considerable 
variations must be expected, yet such variations are within certain 
limits, and that a record of forty years will give a mean from which 
the mean of any other similar period will hardly depart more than a 
few percent. While geological research shows conclusively that great 
changes in climatic conditions have taken place in times past, and un- 
doubtedly will take place in the future, yet these changes have occu- 
pied thousands of years ; and while the records of centuries may show 
radical variations in rainfall conditions, yet so far as the life of man is 
concerned, the variations in annual rainfall are due essentially to the 
great swing in the pendulum of conditions, the cause of which we 
know not, but which we can confidently expect when extremes are 
reached to gradually revert to the opposite conditions. In other words, 
it is clearly evident that so far as the life of man is concerned, the 
rainfall conditions remain essentially unchanged except for the varia- 
tions from average conditions, the extent of which can be fairly well 
established by an examination of available records. In the changes 
of ages, the character of which we have not sufficient data to recog- 
nize, mankind has no practical interest. 

107. Detail Study of Local Variation in Annual Precipitation. — 
Having briefly discussed the general variations in annual rainfall, a 
better idea of the subject may be secured by examining the rainfall of 
a smaller territory in greater detail, and for this purpose the State of 
Wisconsin has been selected. Fig. 118, page 213, shows both the 
actual departure from the mean for the recorded period or rainfall 
observations at various stations in or near Wisconsin, and the pro- 
gressive mean during such period. It will be here noted that the 
variations in the annual rainfall, even in the limited area considered, 
are not synchronous. The period of maximum rainfall at Milwaukee 
was from 1874 to 1879, while at Madison it was from 1878 to il 



Detail Study of Local Variation. 



213 



While in some cases a certain similarity exists in the progressive mean, 
in no two cases are the variations uniformly parallel. The records of 
precipitation show not only a considerable variation in the annual 
amount, but also show that the annual distribution throughout the 



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Fig. 118. — Annual Rainfall and Progressive Means for Wisconsin Stations 

(see page 208). 



state is never the same. It is seen from these cuts that the rainfall 
does not only vary from year to year at any given locality, but the 
variations in adjoining localities are often in opposite directions. As 
the variations in runoff from any drainage area must be due to varia- 
tion in the rainfall at all points on such area, the data from which the 
net results must be deduced are, from any extensive drainage area, 
•consequently very complex. 



214 



Annual Rainfall in the United States. 



The variation in the total quantity of the annual precipitation on 
any drainage area is frequently very great, although it is usually less 
so than at any particular station. At Madison (see Fig. 119) in 
the last twenty-five years, the extreme variations in the total annual 
rainfall have been from a minimum of thirteen inches to a maximum 




Fig. 119. — Variation in Annual ^Rainfall at Madison, Wis. 



of fifty-two inches, the minimum being only twenty-five per cent of 
the maximum. Broadly speaking, such a variation is unusual, for, as 
a general rule, in the upper Mississippi Valley the minimum rainfall 
is usually about fifty per cent, of the maximum. 

108. Cycles in Rainfall. — It has sometimes been pointed out when 
considering the variation in the total annual precipitation that these 
variations occur in a more or less definite cycle. Such cycles depend 
upon the regularity of the recurrence of factors producing precipita- 
tion. The great variations which sometimes occur in cycles of more 
or less regularity are apparently very dissimilar in different areas and 
are produced by great cosmic changes of which little is known. A 



Cycles in Rainfall. 215 

general cyclic character can be roughly traced in some of the curves 
shown in Fig. 117. In this figure the progressive mean for the three 
sections of the United States east of the Mississippi River, was cal- 
culated from the averages of the rainfall observations at several locali- 
ties in the sections mentioned. 2 The cycle as far as it can be de- 
veloped for the southern New England States is of ten-year periods; 
that for the upper Ohio Valley for eight-year periods ; and that for 
Wisconsin for a twelve-year period. Such cycles, however, seem to 
be of too indefinite a character and have too great a local difference to 
be of any value in the prognostications of future conditions. This 
fact is especially true when the actual variations in the annual rainfall,, 
as well as the progressive mean, are shown, as is the case in Fig. 118.. 
As might be inferred from the maps shown in Figs. 112 and 113, there 
is no uniformity in either maximums or minimums prevailing within au 
limited locality, and the cycle is therefore of little practical utility in. 
the consideration of engineering problems. 

109. Extreme Variations in Local Annual Rainfall. — A knowledge 
of the variations to be expected in the annual rainfall of any locality, 
and the length of time required to make rainfall records a safe basis- 
for future estimates, is of much interest in regard to many water 
supply problems. This subject was studied in great detail in a paper 
by Alexander A. Binnie, 3 and he shows graphically (Fig. 120, page 
216) the average deviation from the mean annual rainfall for periods 
of observation extending from one year to thirty-five years as de- 
termined by his studies. It should be especially noted that the devia- 
tions shown are average deviations and that the maximum and mini- 
mum deviations at any single location are materially different. (See 
Table 15). 

In the first part of this table the irregularities in the forty, forty-five 
and fifty year periods are due to the fact that the number of records 
from which these deviations were calculated was very small. 

Binnie's paper contains a large amount of valuable information, and 
represents a large amount of labor in its compilation and treatment; 
it is unfortunately somewhat in error on account of the fact that the 
author divided his data into only single sets of periods instead of mak- 
ing all possible combinations. For example, in an eighty-year group,, 
sixteen five-year consecutive periods were used for comparison where 
seventy-six groups were possible, and instead of eight ten-year groups,, 
seventy-one were possible. 



- Bulletin No. 425, University of Wisconsin, "The Flow of Streams, etc." 
3 Institute of Civil Engineers, Vol. 109, 1891, pages 89 to 172. 



216 



Annual Rainfall in the United States. 



Ordinarily it would be found that among this greater number of 
combinations, greater discrepancies from the mean rainfall would be 
found than are shown by the author, as pointed out by Mr. Blanf ord, and 
in general Mr. Binnie's paper and diagram will therefore show some- 
what less deviation of the average of short-time records from the real 



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Datum Line of Mean Pamfc 












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40 


















































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/£ 20 

years 



35 



Fig. 120. — Average Deviation from Mean Annual Rainfall, by Binnie (see 

page 215). 



mean annual rainfall than will probably be found in many extreme 



cases. 



no. Expectancy of Future Rainfall Occurrences. — The future 
must be judged by the past, and the study of rainfall variations is gen- 
erally for the purpose of judging what extremes must be expected in 
the future. The occasional occurrence of more extreme conditions 







5 


10 


15 


20 


Max. 


Dev. above Mean. . 


32.1 


19.3 


11.9 


11.6 


Max. 


Dev. below Mean.. 


30.4 


18.9 


15.5 


12.9 


Ave. 


Dev. above Mean. . 


17.61 


9.67 


5.59 


4.43 


Ave. 


Dev. below Mean. . 


16.09 


9.62 


6.57 


5.11 


Min. 


Dev. above Mean. . 


6.8 


1.0 


1.1 


0.0 


Min. 


Dev. below Mean . . 


7.8 


4.7 


0.8 


0.0 




16.85 


9.64 


6.08 


4.77 


Extn 


erne Dev. from Ave. 


16.15 


9.66 


9.42 


8.13 



Extreme Variations. 2 1 7 

TABLE 15. 

Deviations from the Mean Value of the Annual Rainfall During the Period 
of Record — Expressed in Percentages of the Mean Local Rainfall as De- 
termined by A. R. Binnie. 

From 4~ Records of from 50 to 97 Years 

25 30 35 40 45 50 

9.9 9.2 7.1 5.7 4.8 3.8 
10.7 9.7 7.7 5.1 2.9 4.1 

3.43 2.91 2.41 3.23 2.60 2.72 

3.78 3.16 2.20 2.21 1.34 2.33 

0.0 0.0 0.0 0.3 0.7 1.5 

0.0 0.0 0.0 0.0 0.1 0.0 

3.60 3.02 2.30 2.77 1.96 2.52 

7.10 6.67 5.40 3.28 2.83 1.58 

From 26 Records of from 50 to 60 Years 



Max. Dev. above Mean 23.2 

Max. Dev. below Mean 29.6 

Ave. Dev. above Mean 15.35 

Ave. Dev. below Mean 14.51 

Min. Dev. above Mean 6.8 

Min. Dev. below Mean 7.8 

Average Deviation 14.93 

Extreme Dev. from Ave 14.67 

than have hitherto been experienced is a warning that as time passes 
even still greater variations must be expected. 

A graphical analysis of the annual rainfall at Madison, Wisconsin 
(Table 20, p. 238), is shown in Fig. 121. In this figure the two limiting 
horizontal lines show the extreme maximum and minimum annual rain- 
falls in the 48 years of record, namely 52.93 and 13.49 inches. The 
next highest and lowest annual rainfalls, namely 49.19 and 20.17 inches, 
are platted on the 24-year ordinate point as representing the next in 
magnitude of the two highest or lowest occurrences in 48 years, and 
therefore, the limit above and below which two annual rainfalls must be 
expected within 24 years. In the same manner the least and greatest of 
the three highest and lowest rainfalls that have occurred in the 48 years 
of experience are platted on the 16-year ordinate, and so on throughout 
the table, the points platted furnishing a guide for the establishment of 
the lines marked "lower limit of maximum experience," and "upper limit 
of minimum experience." The shaded area between these lines and 



10 


15 


20 


25 


30 


35 


14.9 


9.2 


5.1 


7.3 


5.2 


4.5 


16.1 


12.5 


9.2 


9.0 


6.9 


4.7 


8.08 


3.87 


2.47 


2.50 


2.17 


1.73 


8.37 


5.64 


4.08 


2.94 


2.37 


1.86 


1.0 


0.0 


0.0 


0.0 


0.0 


0.0 


4.7 


0.8 


0.0 


0.0 


0.0 


0.0 


8.22 


4.75 


3.24 


2.77 


2.26 


1.78 


7.88 


7.75 


5.95 


6.25 


4.64 


2.72 



218 



Annual Rainfall in the United States. 



the horizontal lines first mentioned sIioavs the limiting field of the ex- 
perience in Madison. 

The "mean curve of maximum experience" and the "mean curve of 
minimum experience" are the curves drawn through the means of the 
one, two, three, four, etc., highest and lowest records respectively, in 
accordance with the data shown in Table 16. 



84-/2 



frequency 
2 




/6 20 24 28 32 
Years of Exper/'ence 

Pig. 121. — Graphical Analysis of Rainfall Experience at Madison, Wis. 

The limiting curves above noted are platted from Columns 2 and 3 of 
this Table, and the mean curves are platted from Columns 5 and 6. 
This diagram shows that based on past experience a maximum rain- 
fall of 52.93 inches should be expected in 48 years ; that in 24 years two 
maximum rainfalls must be expected of 49.19 inches or more, averaging 
51.06 inches, etc. 

The prolongation of this curve which is expanding from the average 
in both directions, would indicate that as time passes greater and lesser 
annual rainfalls must be expected and an estimate of such intensity may 



Expectancy of Rainfall Occurrences. 



219 



be made by prolonging the curve. Such a use of the data is, however,, 
extremely dangerous as it is evident that with any gradual increase, if 
the time is sufficiently prolonged, a minimum of zero would be reached 
on one hand and an infinite rainfall on the other, both of which are ab- 
surd. Judgment would indicate that such curves must ultimately be- 
come parallel with the base when the most extreme conditions are 
reached, but what those extreme conditions are, is indeterminate. 



TABLE 16. 

Experience Table of Annual Rainfalls at Madison, Wis. 

Rainfalls in Number Mean 

Order Order of of Annual 

of Magnitude Annual Rainfall 

Magnitude Inches Rainfalls Inches 

Maximum Minimum Averaged Maximum Minimum. 

1 52.93 13.47 1 52.93 13.49 

2 49.19 20.17 2 51.06 16.83 

3 46.72 20.24 3 49.61 17.97 

4 42.89 22.44 4 47.93 19.90 

6 40.58 22.80 6 45.57 20.29 

8 38.89 24.24 8 43.98 21.13 

12 36.98 25.67 12 41.81 22.43 

16 35.21 28.13 16 40.28 23.70 

24 31.25 31.25 24 37.60 25.66 

Mean Annual Rainfall, 31.63. 

Fig. 121 also contains a maximum and minimum probability curve 
which is discussed in Section in. 

Such curves, while instructive, can not safely be used for estimating 
future occurrences except within wide limits. This is well shown by 
comparing the three experience curves of the annual rainfall at Boston, 
Massachusetts, shown in Fig. 122, p. 220. In this case, 100 years of 
observation are available and curves have been drawn for the 50 years 
from 1818 to 1867 and from 1868 to 1917, both inclusive, as well as for 
the entire 100 year period. 

From Fig. 122 it will be seen that during the first 50 years both the 
maximum and the minimum rainfalls for the entire 100 years were ex- 
perienced, and the occurrence of that period could not be inferred from 
the experience curve for the last 50-year period. The curve for the last 
50 years if taken by itself would indicate that the minimum rainfall had 
been reached in that period, but the curve of the first 50 years shows that 
such was not the case and that even a lower rainfall must be expected. 

in. Rainfall Data and the Law of Probabilities. — Rainfall and 
other meteorological and hydrological data can be studied to advantage 
on the basis of the Laws of Probabilities. The method has been 



220 



Annual Rainfall in the United States. 




25 



O /O 20 30 40 SO SO 70 SO 90 /OO 

Years 

Pig. 122. — Graphical Analysis of Rainfall Experience at Boston, Mass. 



utilized in certain extended investigations by Mr. Allen Hazen, Mr. 
Thorndike Saville and others, and the methods are described in some 
detail in the references given. From Saville's paper, or from any 
work on Least Squares, it appears that* if 

Z = most probable value of a term in a series of observations or the 

mean of such observation, 
n = number of observations. 
M = any observation. 

v = variation of a single observation from the mean, 
r = probable variation of a single observation. 
R = probable variation of the mean. 
2 = summation; then 

2M 
Z = = mean 



n 



■ = 0.6745 J Zy ~ — 

* n — 1 



probable variation of any single observation 



Law of Probabilities. 



221 



R 



: — — == 0.6745,./ __ = probable variation of the mean 

Vn V n (n — 1) 



/ SV2 _ 


V n-1 
r n — 1 



standard variation 



coefficient of variation. 



SM 



In Table ly the annual rainfalls of Madison for 48 years of record 
are shown in the order of their magnitude. The difference (v) and 



to 20 30 4Q 50 6Q 7Q 8Q 90 



99 



933 9999 



\50 























































































































































































































































































































































































































































X 




































































































- 




























































































■** 












































































































< 

































































































































































.^40 

x 

\30 



.Of ./ / IO BO 30 40 50 40 30 20 10 1 I Ol 

Fercenftatje of Years 

Fig. 123.— Probabilities of Annual Rainfall at Maidson, Wis. (Probability 

scale) ' (see page 197). 

the square of the difference (v 2 ) and the percentage of the time which 
the equivalent rainfall is below the amount given in the first column, 
are also given. From this table a probability curve is platted on the 
Hazen probability paper (Fig. 123). 

Each point in the order of its magnitude is platted in the center of a 
strip of width (in per cent.) proportional to the ratio of 100% to the full 

100 
number of terms used, i. e. ; in this case each strip will occupy ■ 



222 



Annual Rainfall in the United States. 



or 2.08%, and the first and last terms will be at absissa 1.04%, the dis- 
tance between points being 2.08% in each case. (Fig. 123.) 

If the data corresponds essentially with the normal law of error, the 
platted points will lie approximately in a straight line. In this case the 
points fall on a curve which departs somewhat from the straight normal 
line of errors and is indicated by the curve which very closely approxi- 
mates the rainfall observation at Madison. From these lines the fre- 
quency of the occurrence of any given amount of annual rainfall at 
Madison can be determined from the principle that the frequency or 
number of years during which a given rainfall will occur once is equal 
to the ratio of unity to the percentage of time in which such occurrence 
has taken place. The relations for Madison, as determined from this 
curve, are shown in Table 18. 





TABLE 


17. 




Yearly 


Variations 


Variations 


Per cent. 


Rainfall 


from the 


Squared 


of total 


inches 


mean 




Time 


in order 






Cumulative 


of magnitude 






Total 


13.49 


18.14 


329.07 


1.04 


20.17 


11.47 


131.56 


3.12 


20.24 


11.39 


129.73 


5.21 


22.44 


9.19 


84.46 


7.29 


22.58 


9.05 


81.90 


9.37 


22.80 


8.83 


77.96 


11.46 


23.06 


8.57 


73.45 


13.54 


24.24 


7.39 


54.61 


15.62 


24.37 


7.26 


52.71 


17.71 


24.59 


7.04 


49.56 


19.79 


25.49 


6.14 


* 37.70 


21.87 


25.67 


5.96 


35.52 


23.96 


26.81 


4.82 


23.23 


26.04 


27.49 


4.14 


17.14 


28.12 


27.67 


3.96 


15.68 


30.21 


28.13 


3.50 


12.25 


32.29 


28.17 


3.46 


11.97 


34.37 


28.78 


2.85 


8.12 


36.46 


28.78 


2.85 


8.12 


38.54 


29.05 


2.58 


6.66 


40.62 


29.45 


2.18 


4.75 


42.71 


30.29 


1.34 


1.80 


44.79 


30.83 


0.80 


0.64 


46.87 


31.25 


0.38 


0.14 


48.96 


"31.25 


0.38 


0.14 


51.04 



Law of Probabilities. 



223 



TABLE 17 — Continued. 



Yearly 


Variations 


Variations 


Per cent. 


Rainfall 


from the 


Squared 


of total 


inches 


mean 




Time 


in order 






Cumulative 


•of magnitude 






Total 


31.35 


0.28 


0.08 


53.12 


31.46 


0.17 


0.03 


55.21 


31.91 


0.28 


0.08 


57.29 


32.32 


0.69 


0.48 


59.37 


32.38 


0.75 


0.56 


61.46 


32.72 


1.09 


1.19 


63.54 


34.40 


2.77 


7.67 


65.62 


35.21 


3.58 


12.82 


67.71 


35.33 


3.70 


13.69 


69.79 


36.04 


4.41 


19.45 


71.87 


36.15 


4.52 


20.43 


73.96 


36.98 


5.35 


28.62 


76.04 


37.10 


5.47 


29.92 


78.12 


37.53 


5.90 


34.81 


80.21 


38.23 


6.60 


43.56 


82.29 


38.89 


7.26 


52.71 


84.37 


39.54 


7.91 


62.56 


86.46 


40.58 


8.95 


80.10 


88.54 


41.13 


9.50 


90.25 


90.62 


42.89 


11.26 


126.79 


92.71 


46.72 


15.09 


227.70 


94.79 


49.19 


17.56 


308.36 


96.87 


52.93 


21.30 


453.70 


98.96 



Total 1,518.07 
Mean 31.63 

Median 31.25 



2,864.43 



Most probable value of annual rainfall 



1518.07 



48 



31.63' 



Standard variation 



V 



2864.43 



(48 — 1) 

7.807 

•Coef. of variation = = 0.2468. 

31.63 

Probable error of a single observation = 0.6745. 7.807 = 5.266. 

5.266 



Probable error of the mean 



= 0.760. 



V48 



100 



P*er cent, of total time represented by each observation 



2.0833. 



48 



224 Annual Rainfall in the United States. 





TABLE 


18. 




Probabilities of Rainfall at Madison, Wisconsin. 




A.mount of Rainfall 


Relative Time 


Equivalent Time 


Frequency 


in inches 


of Occurrence 


in year 


Once in 


26— or 36 + 


25 


11.8 


4 years 


24— or 40 + 


15 


7.2 


6.7 


23— or 42 + 


10 


4.8 


10. 


21— or 46+ 


5 


2.4 


20. 


18— or 52 + 


2 


0.96 


50. 


17.5— or 53.5+ 


1 


0.48 


100. 



To determine the limiting rainfalls for a given period the correspond- 
ing ordinates of the percentage of years is found from the equation 

100 

Percentage of years = 

length of period 

-rt. r n ■ 1 , 10 ° 

thus, tor a five-year period the percentage of years is = 20 and 

5 
the ordinates to the curve at the percentage 20 are 37.5 and 25, and 
these figures mean that in a five-year period we should expect on an 
average one rainfall of 37.5 inches or more and one annual rainfall of 
25 inches or less. 

It should be noted that the conclusions shown in Table 18 and platted, 
in Fig. 121, which are based on the data of Table 17 and Fig. 123, when 
near the mean are well established and may be considered as fairly safe 
and conservative, and that as the departures from the mean increase 
the data become more limited and the conclusions are subject to greater 
error. Even the frequency of once in 20 years for rainfalls of 21 inches 
or less and 46 inches or more will likely be found in error where the data 
for 100 years or more are available for study, and the frequency for 
one rainfall of 18 inches or less and of 53 inches or more once in 100 
years is entirely unwarranted because the period is beyond experience. 
Such an estimate is the best that can be made with the data at hand, 
but should not be taken as a dependable prediction. 

It should be noted, however, that this method of investigation shows 
the extraordinary character of the minimum rainfall record and also 
indicates the fact that the three highest rainfalls are somewhat incon- 
sistent with the balance of the record. It should also be noted that a 
calculation of the probable extreme rainfall of once in 100 years by 
this method is more conservative than if based on the extension of the 
limiting curves of the actual experience platted in Fig. 122. This re- 
sults from the eliminating of inconsistencies by this latter method. 



Law of Probabilities. 



225 



If we calculate the frequency of the minimum rainfall of 13.39 i ncnes 
from the curve in Fig. 123, the frequency indicated would be once in 
4,000 years. This must be regarded as an absurd deduction for this 
rainfall had already occurred in 48 years' record and it is possible that 
other years in the next 100 may fall short of this amount, although 
such an event seems improbable from the data available. This method 
cannot safely be used to project estimates far into the future beyond 
the limits of experience. 




Fig. 124. — Hazen's Map of Rainfall Coefficients. 

112. Application of Probability Calculations. — Mr. Allen Hazen 
prepared a map of the United States 4 (Fig. 124) on which he has shown 
the relative variation in the quantity of annual rainfall in various parts 
of the country by means of the coefficient of variation as expressed 
above. Mr. Hazen says : 

"For the eastern part of the United States the records used are suffi- 
cient to show the normal conditions with a fair degree of accuracy. In 
the west the relative variations are greater, the records are shorter and 
the stations often farther apart and the results thus less reliable. 

"The map is to be regarded as a first rough approximation. It 
serves to give a fairly accurate idea of the general conditions of varia- 
tion in annual rainfall in the United States, but in detail it must be 



4 Engineering News, Jan. 6, 1916- 
Hydeology— 15 



-Allen Hazen. 



226 Annual Rainfall in the United States. 

expected that more ample data, or even more complete use of existing 
data by extending the studies to cover everything available, would re- 
sult in changes in the positions of the lines. Such changes are most 
likely near mountains and in about that third of the country nearest 
the Pacific Coast. 

"The coefficient of variation is lowest on the Atlantic Coast. That 
means that one can count on getting more nearly the normal rainfall 
each year; and on the Atlantic Coast the coefficient does not range 
through wide limits. If one's experience were limited to this part of 
the country, he might almost neglect the range and assume that there 
was everywhere the same chance of a very dry year, such, for example, 
as is represented by a rainfall of only sixty per cent of the normal. 
This is in general the conclusions reached by Binnie for the data 
studied by him. It does not hold, however, for the whole United 
States. As one goes west, the coefficient of variation in annual rain- 
fall increases ; that is to say, the chance of a very dry or a very wet 
year (relatively) is increased. 

"In New York the coefficient of variation is 0.15; at San Francisco 
it is 0.30. This means that on an average the relative variations in 
annual rainfall at San Francisco are twice as great as at New York. 
A year forty per cent short of the normal rainfall comes as often at 
San Francisco as one twenty per cent short of the normal comes in 
New York. 

"By following this method of investigation it will not be hard to 
find quite definitely just how often, on an average, a year of any as- 
sumed relative wetness or dryness will come, and also to find what the 
chances are of years of any degree of dryness coming within a given 
period. 

"Other things being equal, the variations to be expected in any pe- 
riod at different localities will always be in direct proportion to the 
coefficients of variations in the respective places." 

LITERATURE 

GENERAL SUBJECT OF RAINFALL 

U. S. Weather Bureau. Annual Peports and Monthly Climatological Data, 

Monthly Weather Reviews. 
Meteor ologische Zeitschrift. 

Zeitschrift cles Oesterreichischen Gesellschaft fur Meterologie. 
Symon's Meteorological Magazine. 

Annucine de la Soeiete Meteorologique de France, Paris. 
The Royal Meteorological Society of Great Britain. Quarterly Journal. 



Literature. 227 

Laws of Rainfall and Its Utilization, Thomas Hawksley. Proc. Inst. C. E., 

Vol. 31, pp. 53-59. 1871. 
Tables of Mean Annual Rainfall in Various Parts of the World, Alex R. Bin- 

nie. Proc. Inst. C. E., Vol. 39, pp. 27-31. 1874. 
Tables and Results of the Precipitation of Rain and Snow in the U. S., C. A 

Schott. Smithsonian Contribution to Knowledge, No. 222. 
Charts and Tables Showing Geographical Distribution of Rainfall in the U. S. 

U. S. Signal Service Professional Paper No. 9. 1883. 
Rainfall Observations at Philadelphia. Reports Phila. Water Bureau, 1890- 

92. Eng. Record, 1891, p. 246. 1892, p. 360. 
Mean or Average Rainfall and the Fluctuations to which It is Subject, Alex. 

R. Binnie. Proc. Inst. C. E., Vol. 119 (1892), pp. 172-189. 
Rainfall and Snow of the United States, M. W. Harrington. Bulletin C, U. 

S. Weather Bureau, 1894. 
Rainfall of the United States, A. J. Henry. Bulletin D, U. S. Weather Bu- 
reau, 1897. 
Variation in Annual Rainfall, Allen Hazen. Eng. News, Vol. 75, 1916, p. 4. 
Rainfall Data Interpreted by Laws of Probability, Thorndike Saville. Eng. 

News, Vol. 76, 1916, p. 1208. 
The Probable Growing Season, W. G. Reed. Month. Weath. Rev., Sept., 1916. 
Elementary Notes on Least Squares, the Theory of Statistics and Correlation 

for Meteorology and Agriculture, C. P. Marvin. Month. Weath. Rev., 

Oct., 1916, p. 551. This article also contains a bibliography on the subject 

of probabilities and statistical methods. 
The Average Interval Curve and its Application to Meteorological Phenomena, 

W. J. Spillman, H. R. Tolley and W. G. Reed. Mon. Weath. Rev., Apr., 

1916, p. 197. 

Frequency Curves of Climatic Phenomena, H. R. Tolley. Mon. Weath. Rev., 

Nov., 1916, p. 635. 
Predicting Minimum Temperatures, J. W. Smith. Mon. Weath. Rev., Aug., 

1917, p. 402. 



CHAPTER X 

SEASONAL RAINFALL IN THE UNITED STATES AND ITS 

VARIATION 

113. Seasonal Variation in Rainfall. — Climatic conditions are, in 
a general way, fairly consistent, and as the seasons change, conditions 
obtain favorable or unfavorable for precipitation. The maximum and 
minimum monthly rainfall occurs, therefore, at every locality at fairly 




Fig. 125. — Seasonal Rainfall of the United States. 

definite periods. Rainfalls vary considerably from year to year, but 
have, nevertheless, the same general character. The mean seasonal 
distribution of rainfall in the United States and the percentage of the 
annual precipitation that commonly falls during the wet season of the 
year, are shown in Fig. 125, upon which the radically different occur- 
rence of rainfall in various localities is indicated. 

Fig. 126 shows the percentage of the mean annual rainfall that com- 
monly occurs from April 1 to September 30. It may be noted that the 
high percentage of the rather low rainfall on the Great Plains occurring 
during the growing season is a condition favorable for agriculture. 



Seasonal Variations. 



229 



Fig. 127, page 230, shows typical fluctuations of the rainfall for vari- 
ous months in the year at a number of places throughout the United 
States ; and more extended types of the monthly distribution of pre- 
cipitation in the United States are shown in Fig. 128, page 231. 

In Fig. 128 the monthly averages of a number of stations have been 
reduced to percentages of the average annual fall. The character of the 
monthly distribution varies widely at different locations, but will be seen 




Fig. 126. — Percentage of Mean Annual Rainfall Occurring from April 1 
September 30 (see page 228).* 



to 



to have a similar character wherever similar conditions prevail. Thus 
the New England States present a similarity in the distribution of the 
monthly rainfall. A similarity in the monthly distribution is also 
found throughout the lake region and the Ohio Valley. The monthly 
distribution throughout the Great Plains is also similar, and a marked 
similarity exists at points along the Pacific Coast, although the actual 
amounts of precipitation may and do vary quite widely over these same 
areas. 

An examination of the diagram will at once show the wide variation 
in the distribution of rainfall through the growing or crop season in the 
various districts. 

Irrigation in Italy, South Africa and several other countries, is 
made necessary because the amount of rainfall during the growing 
season is deficient, although the annual precipitation may be and fre- 



*Monthly Weather Review, July, 1917. 



230 



Seasonal Rainfall in the United States. 



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231 



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232 



Seasonal Rainfall in the United States. 



quently is as much or more than occurs in places which enjoy a quantity 
of rainfall adequately ample to support agriculture. Milan, the center 
of the irrigated district, has an average annual rainfall of slightly 
more than forty inches. 

This condition of insufficient rainfall during the summer months is 
occasioned principally by the effect of the prevailing winds, coupled 
with the seasonal land temperatures. 




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Fig. 129. — Fluctuations of Monthly Rainfall at Madison, Wis. 

The North Pacific Coast, which receives the major portion of its an- 
nual precipitation during the winter, undergoes this condition because 
of the greater cooling effect of the land at this season upon the westerly 
ocean breezes. 

114. Local Variations in Seasonal Distribution of Rainfall. — The 
total amount of the monthly rainfall is subject to much wider variation 
than that of the annual rainfall as might normally be expected from 
the nature of the occurrence of precipitation. These monthly amounts 
differ very largely from year to year and are subject to such wide 



Local Variations in Distribution. 



233 



TABLE 19. 
Precipitation at Madison, Wisconsin. 



Year 


Jan. 


Feb. 


Mar. 


April 


May 


June 


July 


Aug. 


Sept. 


Oct.' 


Nov. 


Dec. 


Total 


1869 


2.69 
3.35 
2.32 
1.20 
I 40 
3.64 
1.10 
2.31 
1.00 
C.40 
0.79 

2.75 
2.05 
1.33 
1.01 
1.68 
2.44 
3.33 
3.09 
1.74 
1.59 

1.81 

1 19 
2.42 
1.06 
0.96 
1.12 
0.8i 
2.22 
3.59 
0.16 

0.69 
0.62 
0.17 
0.11 
0.30 
0.77 
2.80 
1.89 
0.97 
2.33 

2.82 
0.60 
0.58 
1.64 
0.70 
2.05 
3.07 
1.64 


2.35 
1.35 
1.43 
0.40 
0.60 
0.95 
2.80 
1.60 
0.30 
1.19 
2.54 

1.75 
5.42 
1.74 
1.64 
2.12 
0.82 
2.35 
4.34 
1.01 
1.84 

2.01 
1.38 
1.94 
1.05 
0.46 
0.26 
0.32 
0.92 
2.42 
0.42 

1.26 
0.59 
1.46 
1.11 
1.87 
1.28 
0.97 
0.28 
1.79 
1.70 

0.74 
3.40 
1.50 
1.12 
0.92 
2.30 
0.39 
1.51 


0.79 
3 85 
2.96 
2.18 
2.07 
0.9") 
0.90 
2.27 
3.40 
2.45 
1.34 

2.11 
4.34 
4.73 
0.32 
2.31 
0.62 
4.67 
2.14 
2.61 
1.48 

2.38 
3.62 
1.38 
2.29 
1.73 

o'fa 

2.38 
2.67 
1.94 

1.32 
2.77 
0.60 
3.50 
2.44 
1.74 
2.13 
1.80 
1.62 
1.12 

0.14 
0.47 
1.92 
2.41 
1.J5 
0.87 
2.93 
2.02 


3.08 

0.18 

2.00 

1.82 

1.26 

1.26 

1.87 

2.65 

T 

2.87 

3.33 

5.48 
1.50 
4.21 
1 29 
4.51 
3.45 
2.48 
0.96 
1.85 
1.71 

2.22 
1.45 
3.94 
4.53 
3.57 
1.06 
4.91 
2.51 
2.46 
2.69 

1.31 
0.45 
1.1/' 
2.88 
1.39 
1.43 
0.90 
3.00 
4.41 
7.19 

4.56 
2.44 
1.48 
1.54 
1.84 
0.92 
3.51 
2.45 


4.9:1 

1.09 
3.31 
2.83 
3.53 
2.14 
2.61 
5.18 
1.02 
4.64 
3.91 

4.45 
4.25 

2.89 
6.98 
4.21 
1.68 
2.02 
2.12 
3.76 
3.28 

5.03 

1.48 
6.98 
2.28 
3.36 
2.58 
6.31 
0.51 
4.71 
4.92 

1.86 

2.41 
5.16 
4.38 
5.03 
6.40 
3.35 
2.69 
5.38 
2.49 

2.82 
2.63 
6.57 
6.63 
5.97 
5.98 
2.38 
3.77 


6.14 
1.92 
4.93 

2 44 
6.60 
2.85 
3.37 
4.57 
4.77 
4.20 
2.80 

9.31 
4.15 
7.76 
7.57 
5.47 
5.11 
1.0S 
1.48 
2.95 
2.00 

7.72 
3.69 
7.61 
6.69 
3.94 
0.59 
2.69 
4.03 
4.40 
Z. 64 

3 20 
2.40 
4.27 
1.39 
2.85 
2.b8 
4.55 
2.80 
1.80 
0.29 

1.31 
3.64 
1.13 
3.73 
3.46 
1.75 
4.52 
3.80 


3.63 
5.25 
2.11 
1.26 

0.82 
5.00 
0.97 
4.25 
3.84 
7.56 
5.91 

6.00 
9.47 
2.70 
8.89 
8.44 
7.30 
0.79 
5.49 
2.26 
2.12 

1.81 
2.66 
2.32 
4.64 
1.75 
1.21 
3.62 
1.79 
2.83 
3.22 

6.91 
1.54 
8.98 
6.70 
3.27 
2.27 
1.80 
5.84 
2.85 
2.78 

81 
1.68 
5.63 
8.47 
1.49 
5.04 
2.66 
3.93 


5.92 
3.85 
3.35 
2.24 
2.76 
1.40 
2.56 
3.42 
3.76 
4.28 
0.99 

5.90 
0.56 
6.83 
2.74 
4.39 
6.41 
5.05 
3.75 
1.27 
0.72 

4.23 
1.41 
3.43 
1.42 
0.54 
2.08 
2.43 
2.73 
2.56 
3.57 

2.72 
1.33 
0.78 
6.95 
3.2>» 
2.48 
7.56 
3.59 
2.53 
4.39 

6.56 
3.78 
3.16 
1 59 
3.60 
4.39 
4.24 
3.32 


2.6S 
4.00 
0.47 
5.11 
2.54 
5.46 
2.08 
3.41 
0.64 
6.54 
2.79 

4.44 
8.17 
1.91 
2.39 
4.25 
4.05 
2.29 
6.67 
1.04 
1.93 

2.62 
0.38 
3.. .9 
2.67 
4.21 
0.91 
4.29 
1.73 
2.43 
3.35 

2.89 
4.16 
4.18 
3.54 
5.93 
0.58 
2.04 
4.69 
0.7S 
2.20 

1.83 
5.b5 

5.62 
4.32 
3.49 
10.69 
5.73 
3.48 


2.66 
2.09 
3.07 
0.60 
1.96 
1.44 
1.96 
1.59 
4.12 
3.78 
2.50 

1.68 
9.12 
4.14 
3.79 
4.60 
2.37 
2.21 
3.18 
1.68 
T 

4.59 
1.49 
0.36 
1.85 
1.77 
0.58 
3.03 
0.86 
3.08 
1.58 

4.44 
2.49 
1.23 
ii.18 
1.60 
2.25 
2.69 
l.<4 
0.64 
0.91 

0.63 
2.92 
2.49 
2.53 
3.09 
0.48 
2.97 
2.34 


2.05 
0.53 
1.35 
0.76 
2.15 
3.51 
0.40 
2.31 
2.81 
0.76 
6.02 

1.C8 
2.56 
2.62 
2.56 
1.53 
2.74 
1.21 
1.16 
1.32 
1.17 

1.94 
3.31 
1.24 
1.30 
1.65 
1.03 
1.40 
1 35 
55 
0.96 

1.72 
0.46 
1.41 
1.07 
0.03 
2.23 
2.36 
1.22 
2.14 
a. 28 

1.59 
3.56 
0.89 
1. .3 

0.70 
3.12 
1.69 

1.75 


2.64 

0.67 
1.15 
1.60 
1.80 
0.45 
2.18 
2.59 
2.01 
0.79 
2.29 

1.17 
1.32 
2.03 
1.95 
5.68 
3.59 
1.30 
4.53 
1.57 
2.33 

0.62 
2.24 
2.19 
1.68 
0.67 
1.80 
68 
1.67 
0.21 
1.37 

0.47 
1.02 
1.84 
0.60 
3.34 
1.17 
1.23 
1.35 
0.76 
3.15 

0.56 
1.75 

1.35 
0.33 
1.76 
0.64 
1.24 
1.65 


37 53 


is;o 


28 13 


1871 

i8ta 


29.45 
22 44 


1873 


2} 49 


1874 , .... 
1875 


29.05 
22 80 


1876 


36.15 


1877 


27.67 


1878 


39 54 


1879 


35.21 


1880 

1881 


46.72 
52.91 


1882 

1883 


42.89 
41.13 


1884 


49.19 


1885 


40.58 


1886 


28 78 


1887 

1888 


38.89 
23.06 


1889..... ; 


20.17 


1890..... 


36.98 


1891 

1892 


24.24 
37.10 


1893 


31.46 


1894 


24.59 


1895 


13.49 


1896 


31.35 


1897 


22.58 


189S 


31.91 


1899 ,, 

1 900 


26.81 
28.78 


1901 


20.24 


1902 


31.25 


19D3 


34.40 


lt'Ol 


31.25 


1905 . 


25.49 


1906 


32.38 


1907 


30.29 


1908 


25.67 


ly09 


30.83 


1910 


24.37 


1911 


32.72 


1912 


32.32 




36.04 


1914 


28.17 


1915 


38.24 


1916 


35.33 


Mean for48yrs.. 


31.63 



variations as to sometimes render the character of this occurrence some- 
what obscure, unless a number of seasons are considered, yet the same 
general character ordinarily prevails. 

Figure 129, shows the extreme and the average variation of the 
monthly rainfall at Madison. The monthly rainfall in the various 
months differs widely in amount and is by no means proportional to 
the total annual rainfall for the year. It is especially observable 
that during the year of maximum rainfall, viz: for 1881, the rainfall 



234 



Seasonal Rainfall in the United States. 



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Local Variations in Distribution. 



235 



for April was almost as low as for April of the year 1895 when 
the total annual rainfall was at a minimum. It is also observable that 
the rainfall for August, 1881, was less than the rainfall for August of 
1895. 



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1/57/7 /^e^ M57- ^o/- A/c?y y<y/75 .A//^/ /7<y^ v5e/?/ 0c/ A/ok . Dec 
Fig. 131. — Mass Diagrams of Rainfall at Madison, Wis. (see page 236). 

The percentage of variation in any monthly period is always very 
much greater than for the annual period in the same locality. This is 
very well illustrated by the record of precipitation at Madison, Wis- 
consin. (See Table 19.) Here the monthly rainfall varies from a 
minimum of merely a trace (see April, 1877) to a maximum of 10.69. 
inches (see September, 1915). 



236 



Seasonal Rainfall in the United States. 



115. Mass Diagrams of Rainfall. — The seasonal variations as in- 
dicated by diagrams of average monthly rainfall are more or less arti- 
ficial, as rainfall knows no such limitations. The mass diagram, there- 
fore, will give a clearer indication of the actual occurrence and still 
show its relation to the artificial division of the calendar year. Fig. 
130, page 234, shows mass diagrams of the rainfall at various stations 
throughout the United States for the year 191 1, and gives in greater 




£i/t?ene 
Oregon 



Gr&nr'& f^ass J<3cAsor?t////e 
Oregon Oregon 



7~w/n r~a//s 
/afc7/?o 



Oenver 
Co/orac/o 



Sunny S/'cte 



Fig. 132. — Comparison of Normal Annual and Summer Rainfall of Oregon 
with that of Localities in which Irrigation is Practiced (see page 237). 

detail the comparative distribution of rainfall throughout this year. 
The departure from these typical curves for other years will of course 
be considerable, but the general character and relative distribution do 
not vary greatly even though the total for the year is subject to wide 
variation. Fig. 131, page 235, shows mass diagrams of the occurrence of 
rainfall at Madison, Wisconsin, for years of maximum, minimum and 
average rainfall conditions from which variation in the actual rainfall 
distribution in different years are quite apparent. 

116. Seasonal Divisions of the Year for Agricultural Purposes. — 
For agricultural purposes the divisions of time and of rainfall by years 
and months is not sufficient. Popularly the seasons are divided into: 

Spring: March, April, May. 

Summer: June, July, August. 

Autumn: September, October, November. 

Winter: December, January, February. 



Seasonal Divisions of the Year. 237 

The shortest day of the year is December 22, and if the change in the 
earth's temperature followed immediately on the movement of the sun, 
this date would be mid-winter, and mid-summer would occur on June 
22, which is the longest day of the year. The seasonal changes how- 
ever, lag behind the sun's movements, and the summer months of June, 
July and August are perhaps the most important from an agricultural 
standpoint, although the entire period of plant life would in general in- 
clude April to September inclusive. 

As has already been noted (see Sec. 113), the amount of rain that 
falls in a year is not so important for agricultural purposes as the 
amount that falls during the growing season. Should this season be 
deficient in rainfall, water must usually be supplied for successful agri- 
culture by irrigation. In Fig. 132, page 236, a comparison is made of 
the summer rainfall in certain cities of Oregon, where the annual rain- 
fall is fairly large, with certain locations in the arid regions where irri- 
gation is practiced. It has been found that except in years where a late 
spring rainfall has stored sufficient moisture in the ground for plant 
use, irrigation is also essential in Oregon for the best results. 

The annual and seasonal averages of rainfall for each State and the 
normal variation from such averages as determined by the Weather 
Bureau in 1894 1 are shown in Table 20. These amounts would prob- 
ably be altered somewhat by the more extensive observations that have 
been made up to the present time. 

In 1897, 2 A. J. Henry made a similar and more extended compari- 
son for many stations in the United States for the crop growing season 
from April to September, inclusive. 

117. Further Analysis of Rainfall for Utilitarian Purposes. — That 
annual seasonal or monthly quantitative records of rainfall are not in 
sufficient detail for an intelligent knowledge of its occurrence for utilita- 
rian purposes is obvious from a brief consideration. Hinrich points 
out ("Rainfall Laws," by Dr. Gustavus Hinrich, U. S. Weather Bu- 
reau, 1893) that while the rainfall at Iowa City for 1889 was 28.52 
inches in seventy days, and in 1890 was 27.05, in ninety-seven days, the 
rainfall so expressed might be regarded from such limited data as es- 
sentially identical, but that such a statement was not in accordance with 
facts. 



1 Rainfall and Snow of the United States, M. W. Harrington. Bui. C, 
U. S. Weather Bureau. 

2 Rainfall of the United States, A. J. Henry. Report of the Chief of the 
Weather Bureau for 1896 and 1897. 



238 



Seasonal Rainfall of the United States. 



TABLE 20. 
Annual and Seasonal Average of Rainfall for each State. 



Alabama . 
Arizona .... 
Arkansas ., 
California. 
Colorado ., 



Connecticut 

Delaware 

District of Columbia 

Florida 

Georgia 



Idaho .. . 
Illinois .. 
Indiana . 



Indian Territory. 
Iowa 



Kansas .... 
Kentucky. 
Louisiana. 

Maine 

Maryland . 



Massachusetts . 

Michigan 

Minnesbta 

Mississippi...... 

Missouri 



Montana 

Nebraska 

Nevada 

New Hampshire. 
New Jersey 



New Mexico 

New York 

North Carolina.. 
North Dakota... 
Ohio 



Oregon 

Pennsylvania .. 
Rhode Island . 
South Carolina 
South Dakota. 



Tennessee . 

Texas 

Utah 

Vermont .. 
Virginia.... 



Washington ... 
West Virginia. 

Wisconsin 

Wyoming 



Area in 
square miles. 



Total 

Average . 



52, 250 
113,020 

53, 850 
158, 3G0 
103,925 

4, 990 
2,050 
70 
58, G80 
59,475 

84, 800 
56, 650 
36, 350 
31,400 
56,025 

82, 080 
40, 400 
48, 720 
33, 040 
12,210 

8,315 
58, 915 
83, 305 
46,810 
69,415 

! 46, 080 

77,510 

110,700 

9,305 

7,815 

122,580 
49,170 
52, 250 
70,795 
41,060 

96,030 
45,215 
1,250 
30, 570 
77,650 

42, 050 

265, 780 

84,970 

9, 505 

42,450 

69, 180 

24, 780 
56, 040 
97,890 



Spring. 



2, 985, 850 



Inches. 

14.9 
1.3 

14.3 
6.2 
4.2 

11. 1 
10.2 
11.0 

10.2 
12.4 

4.4 
10.2 
11.0 
10.6 

8.3 



12.4 

13.7 
11. 1 
11.4 

11.6 

7.9 
6.5 
14.9 
10.0 

4.2 

8.9 
2.3 
9.8 
11.7 

1.4 
8.5 

12.9 
4.6 

10.0 

9.8 
10.3 
11.9 

9.8 



13.5 
8.1 
3.4 
9.2 

10.9 

8.6 
10.9 



Summer. 



Inches. 
13.8 
4.3 
12.5 
0.3 
5.5 

12.5 
11.0 

12.4 
21.4 
15.6 

2.1 
11.2 

11.7 
11.0 
12.4 

11.9 
12.5 
15". 

10.5 
12.4 

11.4 
9.7 
10.8 
12.6 
12.4 

4.9 
10.9 

0.8 
12.2 
13. J 3 



10.4 
16.6 
8.0 
11.9 

2.7 
12.7 
10.7 
16.2 

9.7 

12. 5 
8.6 
1.5 
12.2 
12.5 

3.9 
12.0 

11.6 
3.5 



Autumn. 



Inches. 

10.0 
2.2 

11.0 
3.5 
2.8 

11.7 
10.0 

9.4 
14.2 
10.7 

3.6 
9.0 
9.7 
8.9 
8.1 

6.7 
9.7 
10.8 
12.3 
10.7 

11.9 
9.2 
5.8 

10. 1 
9.1 

2.6 
4.9 
1.3 
11.4 
11.2 



9.7 
12.0 
2.8 
9.0 



10.5 
10.0 
11.7 
9.7 



10.2 
7.6 
2.2 

11.4 
9.5 

10.5 
9.0 
7.8 
2.2 



Winter. 



Inches. 

14.9 

3.1 

12. 8 
11.9 



11.5 
9.6 
9.0 
9.1 

12.7 

7.0 

r.7 

10.3 

5.7 
4.1 



11.8 
14.4 

11. 1 
9.5 

11.7 
7.0 
3. 1 

15.4 
6.5 

2.3 
2.2 



2.0 
7.9 
12.2 
1.7 
9. 1 

21.0 
9.5 

12.4 
9.7 
2.5 

14.5 
6.0 

9^3 
9.7 

16. 8 
10.0 



Annual. 



8.6 



Inches. 
53.6 
10.9 
50.6 
21.9 
14.8 

46.8 
40.8 
41.8 
54.9 

61.4 

17.1 
38.1 
42.7 
36.2 

32.9 

31.0 
46.4 
53.9 
45.0 

44.0 

46,6 
33.8 
26.2 
53.0 
38.0 

14.0 

26.9 

7.6 

44.1 

47.3 

12.7 
36.5 
53.7 
17.1 
40.0 

44.0 
42.5 
46.7 
45.4 
22.9 

50.7 
30.3 
10.6 
42. 1 

42.6 

39.8 
42.8 
32.5 
11.6 



Seasonal 
variation. 



Inches. 
1.5 
3.3 
3.9 
40.0 
2.4 

1. 1 
1.1 
1.4 
2.4 
1.5 

3.3 
1.5 
1.-2 
1.9 
3;0 

3.4 
1.3 
1.4 
1.2 
1.3 

1.0 
1.4 
3.5 
1.5 
1.9 

2.1 
5.0 
4.0 
1.2 
1.2 

4.1 
1.3 
1.4 
4.7 
1.3 

7.8 
1.3 
1.2 
1.7 
3.9 

1.4 
1.4 
2.3 
1.3 
1.3 

4.3 
1.4 
2.2 

2.7 



Analysis of Rainfall. 239 

"In 1889 there were seven rain days with over one inch and two with 
■over two inches of rainfall ; in all, nine rain days with excessive rains, 
aggregating 13.02 inches. Of the total rainfall of 28.52 inches only 
15.50 fell in moderate rains, almost the only ones that can benefit the 
growing crops. 

"In the year 1890 only four rain days exceeded one inch of rain, ag- 
gregating 5.88 inches in the entire year. Consequently, of the total 
rainfall of 27.05 inches, only 5.88 inches came in washing and flooding 
rains, and 21.17 inches in moderate showers, beneficial to the farmer. 

"To be quite exact, we ought yet to separate from these beneficial 
rains those that were insignificant. In 1889 there were thirty-nine days 
.aggregating only 1.42 inches, while in 1890 there were thirty-five days 
aggregating 1.15 inches of rainfall." 

The comparison of these data with the twenty-year normal for Iowa 
City is shown in Table No. 21. 

TABLE 21. 

Year 1889 1890 20 Yr. Normal 

• Total Rainfall 28.52 27.05 35.59 

Washing & Flooding Rain (1 in. or more per 

day) 13.02 5.75 15.69 

Insignificant Rains 1.42 1.15 1.45 

Total Useless or Damaging Rains 14.44 7.03 17.14 

Total Utilizable Rain 14.08 20.02 18.45 

From the above it will be noted that so far as they came in the right 
seasons for agriculture, the utilizable rains of 1890 exceeded the nor- 
-.mal, although the annual rainfall was over eight inches sub-normal. 

TABLE 22. 
HinricWs Classification of the Intensities of Rainfall. 
Type Amount Degree 

.01 to .1... Sprinkles or Insignificant Rains. 

Useful for Grass, Grain and Corn. 

1 .1 to .2 Showers. 

2 .2 to .4 Light Rains. 

3 .4 to .8 Soaking Rains 

Excessive or Damaging Rains. 

4 .8 to 1.6 Washing Rains. 

5 1.6 to 3.2 Flooding Rains. 

8 3.2 and up Torrential Rains. 



240 Seasonal Rainfall of the United States. 

118. Seasonal Rainfall as Affecting Stream Flow. — In consider- 
ing the rainfall on a district in relation to the runoff of streams, it is 
desirable to study the rainfall records on the basis of what may be 
termed "the water year." This period will vary somewhat materially 
with the climatic conditions in various parts of the world. In England, 
the water year September i to August 31 is sometimes used. The 
United States Geological Survey is at present (1917) arranging their 
runoff data for a water year from October 1 to September 30. Rafter 3 
has used a water year from December 1 to November 30. He calls 
the first six months of this period, December to May inclusive, the 
"storage" period. June, July and August constitute the "growing" pe- 
riod ; September, October and November, the "replenishing" period. 
For the purpose of discussing rainfall in its relation to runoff it is de- 
sirable to divide the annual rainfall in accordance with such periods 
as may be selected for such purposes. For example, from a study of 
mass diagrams of the annual rainfall at Madison, Wisconsin, the water 
year might be divided as shown in Table 23. 

TABLE 23. 

Logical Division of the Water Year at Madison, Wisconsin. 
WATER YEAR FROM TO 

1903- 4 Oct. 3, 1903 Sept. 28, 1904 

1904- 5 Sept. 28, 1904 Oct. 17, 1905 

1905- 6 Oct. 17, 1905 Oct. 17, 1906 

1906- 7 Oct. 17, 1906 Sept. 16, 1907 

1907- 8 Sept. 16, 1907 Sept. 27, 1908 

1908- 9 Sept. 27, 1908 Sept. 12, 1909 

1909-10 Sept. 12, 1909 Sept. 22, 1910 

1910-11 Sept. 22, 1910 Sept. 28, 1911 

1911-12 Sept. 28, 1911 Sept. 13, 1912 

For small drainage areas in the immediate vicinity of Madison to 
which these mass diagrams of rainfall might apply, a similar division of 
stream flow data might be made although the year for such data might 
logically be started a few days later as the effect of rainfall on stream 
flow is not immediate. For large areas where the rainfall differs ma- 
terially from place to place a combined mass diagram will give a clear 
idea of the actual variations in the beginning of the water year. 

The artificial divisions of daily, weekly, monthly and other periodic 
arrangements of observations are sometimes misleading when they 



3 Hydrology of the State of New York. G. W. Rafter, Albany, 1905. 



Analysis of Rainfall. 241 

are examined with reference to the value of the rainfall so recorded 
for agricultural purposes or with reference to stream flow records. 
A rainstorm follows no such divisions of time, and the effect of a 
heavy rainfall near the end of a period will often result in an increased 
runoff during the following period for which monthly records of ob- 
servations, usually available, offer no adequate explanation. This 
misleading feature of the records of artificial periods should be duly 
recognized ; and for the purpose of detailed hydrological analysis, the 
seasons may better be divided up in accordance with the actual occur- 
rence of the rainfall than on the basis of any artificial division of the 
calendar year. 

In the study of runoff attention must also be given to the amount 
and intensities of occurrence of the rain. Showers and light rains 
(see Table 23) will ordinarily not affect runoff conditions or even 
the ground water during the growing season, as they will ordinarily 
be taken up entirely by vegetation when such exists on the drainage 
area, while such rains will augment the stored waters of the winter 
season. For a comparison of rainfall with the runoff from year to 
year such rainfalls may be eliminated from consideration, either from 
the seasonal amounts or from the mass curves. In certain studies 
in Wisconsin, of rainfall in relation to runoff, single rain storms not 
less than the following amounts were eliminated for various months 
as follows : 

November 08 or less 

Dec, Jan. and Feb all considered 

March and April 10 or less 

May 15 or less 

June and September 20 or less 

July and August 25 or less 

October .12 or less 

The net effect on the annual amounts of rainfall which under the 
above assumptions might be considered as actually influencing stream 
flow or ground storage is shown in Table 24. 
Hydrology — 16 



242 



Seasonal Rainfall of the United States. 



TABLE 24. 
Effect on Annual Rainfall of the Elimination of Showers and Light Rains. 

Estimated Percent- 
Year Actual Effective age Con- 
Rainfall Rainfall sidered 

1904 

1905 

1906 

1907 

1908 

1909 

1910 

1911 

1912 

1913 

1914 

1915 



34.69 


27.82 


80 


30.46 


24.96 


82 


33.96 


28.85 


82 


24.93 


18.36 


73 


28.29 


22.81 


81 


30.70 


24.14 


79 


21.01 


16.20 


77 


38.91 


31.49 


81 


29.88, 


22.99 


76 


30.72 


21.75 


71 


30.40 


20.25 


68 


32.91 


26.78 


82 



CHAPTER XI 
GREAT RAINFALLS 

119. Importance of the Study of Great Rainfalls. — Many engineer- 
ing problems, such as flood protection, the size of sewers, drains and 
ditches for drainage, works, the size of spillways and flood gates in 
dam and other similar engineering projects that are affected by the 
possible maximum flow in streams or from drainage areas of greater 
or lesser extent, are often dependent for their proper solution upon a 
knowledge of the intensity and distribution of the maximum rainfalls 
that must be expected and the flood flow that will result therefrom. 
While the flood volumes in all such cases depend on many factors, the 
most important one is the amount of the rainfall that may occur 'on 
the area under consideration within a given period of time. 

The actual maximum runoff from a given area is always the best in- 
formation to be used as a basis for the solution of such problems. 
Such knowledge is seldom available because runoff data are seldom 
collected until a need for such information arises, when on account of 
the rarity of occurrence of extreme conditions the needed information 
cannot be secured immediately, and the problem must often be solved 
without undue delay. Rainfall statistics for a considerable period of 
time and of more or less value for the solution of such problems are 
usually available at nearby stations or at stations where the conditions 
are sufficiently similar to warrant conclusions based on the same. A 
study of such records therefore often becomes essential, and it is de- 
sirable that such a study be based on a proper interpretation of the 
records and a knowledge of the ordinary, the occasional and the rare 
but extreme conditions that are certain to occur. 

120. Great Rainfalls. — The comparative magnitude of a rainfall 
will depend on three factors, each one of more or less relative im- 
portance, according to the nature of the problem which is under con- 
sideration. These factors are : intensity, duration and area covered by 
the rainstorm. 

Intensity refers to the rate of precipitation or the amount of rain 
falling within a given time. Duration defines the time limit within 
which the precipitation takes place, and area defines the geographic 
extent of the storm or of as much of it as may be covered by the 
rains of given intensity and duration. 



244 Great Rainfalls. 

For example, Mr. James B. Francis investigated in some detail the 
great storm that occurred in New England on Oct. 3-4, 1869. 1 He 
found that some of the local rates of intensity and duration were as 
follows : 

TABLE 25. 
Local Intensity and Duration of Rainfall of Oct. 3-Jf, 1869. 
Amount Duration Rate per 24 Hours 

4.00 inches 2 hours 48.00 inches 

4.27 inches 3 hours 34.16 inches 

5.86 inches 18.5 hours 7.61 inches 

7.15 inches 24.0 hours 7.15 inches 

8.90 inches 30.0 hours 7.13 inches 

12.35 inches 48 hours 6.17 inches 

He also found that the total amount of rainfall and the extent of 
area covered by the storms were as follows : 

TABLE 26. 
Amount and Distribution of the Rainfall of Oct. 3-lf, 1869. 
Depth of Rain Area Covered 

6 in. or more 24,431 sq. mi. 

7 in. or more 9,602 sq. mi. 

8 in. or more 1,824 sq. mi. 

9 in. or more 1,046 sq. mi. 

10 in. or more 519 sq. mi. 

11 in. or more 179 sq. mi. 

Another factor which may be of great importance in certain problems 
is frequency. Frequency defines the period of time within which a 
rainfall of a given magnitude may be expected to occur. Experience 
has shown that the most excessive rainfalls occur only rarely, for brief 
intervals and over limited areas, and 'that as the size of the area and 
the length of time considered increase, the magnitude of that which 
must be regarded as excessive rainfall on such areas diminishes. The 
probability that a more excessive rainfall may occur in the future and 
the determination of the frequency of occurrence of storms of any 
magnitude are to a considerable extent dependent upon the length of 
the record and may be treated on the basis of probabilities as described 
for annual rainfall in Sections no and in. 

Experience has also shown that the probability of the occurrence of 
great rainfalls is largely a local problem and that the causes and con- 



1 James B. Francis. Distribution of Rainfall during the Great Storm 
of October 3 and 4, 1869. Trans. Am. Soc. C. E., Vol. 7, p. 224. 



Limitations of Information. 245 

ditions of rainfall vary to such an extent that the nature of the ex- 
treme rainfalls which should be anticipated in one part of the country 
may be greatly different from those which may occur in some other 
parts of the country, where the factors that control their occurrence 
are quite different. Like most other rainfall problems, the problem of 
the occurrence of great rainfalls must be solved on the basis of our 
limited knowledge of the nature of the rainfalls that have occurred in 
the past, either in the same locality or in other localities where similar 
conditions exist and on the assumption that conditions which have ob- 
tained in the past will again be repeated and perhaps exceeded in the 
future. 

121. Limitations of Information. — There are about 4,700 Weather 
Bureau Stations in the United States, approximately equivalent to one 
station for each 632 square miles. These stations are more numerous 
in the thickly settled portion of the country and with few exceptions 
are located at or closely adjoining centers of population. There are 
few stations on mountains or deserts or other uninhabited regions. As 
a consequence of these conditions there are large regions from which 
practically no information is available except such as may be inferred 
from the records of adjoining stations. 

With rain gages scattered at such wide intervals as obtain in even 
the most thickly populated portion of the country, rainfalls of high in- 
tensity but of limited area undoubtedly frequently occur of which no 
records are made, as the area covered is largely or entirely between 
stations. For example, a considerable flood occurred about June 4, 
1916, on Mad Creek about six miles south of LeRoy in western New 
York. 2 The drainage area of the stream was only 1.5 square miles, 
and the maximum flood discharge was estimated at about 2,000 cubic 
feet per second per square mile, a most unusual flood discharge. As 
the slopes tributary to this stream are not particularly steep, it is prob- 
able that such a flood peak would have required a rainfall on the 
drainage area of 12 or more inches in 24 hours, in order to have pro- 
duced the maximum peak. No indication of such a rainfall is shown 
:n the rainfall records. The nearest rainfall station of the U. S. 
Weather Bureau at Avon, New York is about ten and one-half miles 
east of this area and shows a rainfall for June 2 and 3 of 2.58 inches. 

The small area to which many intense storms may be limited is il- 
lustrated by Fig. 133, page 23 1, 3 which shows a ninety minute pre- 



2 See letter from J. P. Wells. Eng. Rec, June 24, 1916, Vol. 72, p. 842. 

3 See The Ohio Water Problems. C. E. Sherman. Bui. No. 15, College of 
Eng. Univ. of Ohio. 



246 



Great Rainfalls. 



cipitation that occurred near Cambridge, Ohio, July 16, 1914. This 
storm chapced to center over the U. S. Weather Bureau Station which 
is located outside of Cambridge. The observer was ready and 
made an accurate measurement of the precipitation, and soon after 
the storm the County Surveyor traced its outline upon the Cambridge 
quadrangle of the U. S. Topographical Survey. In drawing the map 
(Fig. 133) it was assumed that the outline traced represented a rain- 




Fig. 133. — Rainfall in Ninety Minutes at Cambridge, Ohio. 

fall of one-half inch, and the isohyetal lines were proportioned be- 
tween the outline and the station. It should be noted that if the cen- 
ter of this storm had moved five miles in any direction, there would, 
have been no adequate records to give any idea of the intensity, and 
if the center had moved two miles its maximum intensity would not 
have been recorded within 25 per cent, or more. 

On August 24, 1906, an unprecedented rainfall occurred at Guinea, 
Caroline County, Virginia, with an intensity of about 9.25 inches in 
about thirty minutes. This rain accompanied a local thunderstorm 
confined to a limited area. The storm passed over Woodslane, Va., 
about 4 P. M. and the rain at Guinea, about two and five-tenths miles 
from Woodslane, began about 5 130 P. M. and continued for an hour, 
accompanied by heavy thunder and lightning. The storm afterward 
turned northeastward and passed over Corbin, Va., about six miles 
from Guinea. It was not noted at other points, and the territory cov- 



Sources of Information. 247 

ered was apparently not more than ten miles in length. The storm did 
not reach any Weather Bureau station. 4 

It is apparent from the above discussion that many local rain storms^ 
especially such as occur in the mountains, deserts or thinly inhabited! 
portions of the country, are entirely unrecorded and that our informa- 
tion concerning intense storms which cover only small areas is very in- 
complete. 

Table 27, page 248, shows the record of the most intense rainstorms- 
that have been observed in the United States and elsewhere so far as 
could be determined from available records. 

122. Sources of Information. — Unfortunately the rain gages in use- 
in the majority of the stations in the United States are the gages shown 
in Fig. 106 and only furnish information of the rain that has fallen 
during the period which has elapsed since the gage was last read. By 
reading at frequent intervals, the rate of rainfall for brief periods may 
be determined, but in general observations are made only once for- 
each twenty-four hours, and hence the information available from 
such gages is usually only for such period. As intense twenty-four 
hour rainfalls seldom occur within the time included between two read- 
ings, even the most intense rainfall that occurs at a station for such: 
a period is not always ascertainable from the records unless special? 
measurements are made and noted at the time of the occurrence. For 
example, in the heavy rainfall that occurred in July, 19 16, near Alta- 
pass, North Carolina, (see Fig. 96, page 175) the records show that 
the rainfalls on July 15 and 16 were 3.90 and 19.32 inches respectively. 
It was noted however that the maximum precipitation in twenty-four 
hours included the rainfall on a part of both of these days and 
amounted to 22.22 inches, one of the greatest rains that has ever been? 
recorded within twenty-four hours in the United States. 

Fortunately, recording gages are now in use at nearly 400 of the- 
principal Weather Bureau Stations, and many records are available- 
for a considerable term of years from these various stations. Sucfr 
records as are available have for the most part been published in the 
Monthly Weather Review, to which reference must be made for such 
data. When considering storms of a greater duration than twenty- 
four hours, the records of daily rainfall become of value ; but here 
again some uncertainties arise from the different times at which the 
gages are read, and from such records it is impossible to differentiate 
the rainfall for any periods of less than one or more days, and even 



4 Monthly Weather Review, 1906, p. 406. 



248 



Great Rainfalls. 



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Frequency. 



249 



then when comparing stations where the time of reading is different, 
they are to an extent uncertain. Such a study, when it includes all of 
the data which are pertinent to a given locality, will furnish a reason- 
able basis for the estimate of local storm intensity. 

123. Frequency of Intense Rainfalls. — In general the frequency of 
intense rainfalls increases with the increase in the average annual rain- 




4 8/2 

Frequency, Years 

Fig. 134. — Average Frequency and Average Intensity of Maxi- 
mum One Day Storms (see page 250). 

fall of a locality for the reason that the conditions favorable to in- 
tense rainfall are more common under such conditions. For example, 
intense rainfalls are much more common in the State of Florida where 
the average rainfall is about 55" per annum than in the state of Wis- 
consin where the average rainfall is about 32" per annum, or in the 
State of Ohio where the average rainfall is about 36" per annum. 
This condition is due however not only to the conditions favorable 
for rainfalls in Florida but also to the West Indian hurricanes which 
frequently cross that State and which commonly bring about con- 
ditions favorable for torrential rainfall. The rainfalls of Wisconsin 



250 Great Rainfalls. 

and Ohio are a result of the greater cyclonic storms which in general 
are not so productive of brief and intense precipitation. Occasionally, 
however, conditions favorable to high rates of precipitation do occur 
in Wisconsin and Ohio as is evidenced by the intense rainfall of 
July 16, 1914, shown in Fig. 133, page 246, and by the rainfall of 
ii/4" which occurred at Merrill, Wisconsin, within twenty-four hours 
in July, 1912. 

In the semi-arid regions where the average annual rainfall is very 
low, exceedingly intense rains of limited extent, termed cloud bursts, 
occasionally occur. On August 9 to 11, 1909, 13.38" of rain fell at 
Monterey, Mexico, within forty-eight hours, and between August 25 
and 29, 1909, 21.61" of rain fell within ninety-eight hours. The an- 
nual rainfall at this station for 21 years previous to that date averaged 
19.86", and in the four days of the second storm more water fell than 
usually falls in an entire year. 5 It is evident therefore that the in- 
tensity of the local rainfall which may occur bears no direct relation to 
the amount of annual precipitation. 

Figure 134, 6 page 249, is a study of the average frequency and average 
intensity of the occurrence of one-day storms at various selected stations 
where long records, ranging from forty-two years at Galveston to sixty- 
seven years at St. Louis, were available. These curves are constructed 
as follows : For the Galveston curve, based on forty-two years of record, 
the probable maximum storm that will occur each year is taken as 
equal to the average of the forty-two maximum storms that have oc- 
cured during the period, and the average of the twenty-one maximum 
storms is taken as the probable maximum storm that will occur every 
second year. Other points on the curve are established in the same 
manner. 

The flattening of the curves, due to'the close agreement in intensity 
of the several storms in the records which are included in the average 
for the fourteen year period, gives assurance that the curves are typi- 
cal, and that the probabilities that a storm such as is likely to occur 
at Galveston may occur at Cleveland are very remote if not physically 
impossible. 

124. Local Intensities of Short Duration. — The records of intense 
storms of short duration for any locality may be platted with the in- 
tensities as ordinates and with the intervals of time at which such in- 



5 See Eng. News, Sept. 23, 1909. 

6 Prom data furnished by A. E. Morgan, Chief Engineer, Miami Conservancy 
District. See also Eng. News, Vol. 77, p. 150. 



Local Intensities. 



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-Maximum Intensities of Rainfall at St. Paul, Minn. 



tensities have occurred as abscissas. Such a graphical chart of the 
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in the last 29 years (1917) is shown in Fig. 135. The intensi- 



252 



Great Rainfalls. 





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Fig. 136. — Maximum Rates of Local Rainfalls (see page 253). 

ties investigated are those of one inch per hour or greater and for 
intervals of from 5 to 120 minutes. The enveloping line, ABCD^ drawn 
through the points of maximum intensity for each interval, shows the 
absolute maximum experiences of St. Paul within the period for which 
the records are available. Each of the points shown is the maximum 



Local Intensities. 253 

rate for the given interval for a storm in which a rate greater than one 
inch per hour has occurred for such interval, and in some cases one 
point under each interval may represent a single storm. Thus the line 
ECD is the intensity-interval curve for the storm of August 9, 1902, 
and the line ABF is the intensity-interval curve for the storm of June 15, 
1892. These two storms together furnish the maximum records for 
the intensities at St. Paul, while numerous other storms of lesser inten- 
sities are represented by the other points on the diagram. In some 
cases a single storm may be represented by only one point. Where the 
same intensity of rainfall has occurred two or more times at any one 
interval, the fact is designated by a number set opposite the point in 
question. 

Fig. 136, page 252 shows the maximum rates of local rainfalls of 
short duration for various localities throughout the United States, de- 
termined in the same way but covering the period from 1889 to 19 10 
inclusive. 

125. Frequency of Intense Storms of Short Duration. — It will be 
noted that the envelope ABCD (Fig. 135, page 251) is drawn through 
points that are for the most part some distance above the next highest 
points and therefore seems to represent conditions somewhat more 
extreme than should normally be expected for a 29-year period. In 
some cases the extreme storms seem to represent conditions even more 
unusual when the limited period of observation and the 'more frequent 
intensities are considered. Thus in Fig. 137, page 254, where the 
intensity of storms of brief duration at Madison are shown, the storm 
of August 29, 1906, is so far above the storms indicated by the remain- 
ing points as to show clearly that it is not a fair criterion of the limiting 
intensities which should ordinarily be expected to occur within the 13 
years of record (1905-1917). The unusual character of this rainfall 
is also indicated by the comparison shown in Fig. 141, page 258. 

Referring again to Fig. 135, showing the record of intense storms at 
St. Paul, if the various intervals are considered it will be noted that 
there are two storms of one inch per hour or more at the 120-minute in- 
terval or — = .069 storm per year of a greater intensity than one inch 

per hour. At the interval of 100 minutes there are four storms above 
one inch per hour intensity or a frequency of .138 storm per year, etc., 
for each interval. In the same way the storms per year greater than 
1.5 inch, 2 inches, 2.5 inches, etc., per year may be determined and 



254 



Great Rainfalls. 



platted as in Fig. 138, page 255. These points may be connected by 
straight lines thus indicating the absolute results of experience ; or a 
series of smooth curves can be platted through these points which may 




10 



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20 JO 40 50 60 80 

[nfervafe of Time - A4/nu/-e<5 
Fig. 137.— Intensities of Storms of Short Duration at Madison, Wis. (see 

page 253). 

l>e drawn to average the points or to include them all, as the investigator 
may desire. In the case of the smooth curves the indication of fre- 
quency at certain intervals may be somewhat greater or less than the 
absolute experience, but if consistently drawn may possibly indicate 
more nearly the truth which would be 'developed by a longer series of 
observations, by giving greater weight to the preponderance of evidence 
over a single or a few observations which mav be more or less extreme. 



Frequency. 



255 



Having platted the points as above outlined and adjusted the fre- 
quency-interval lines as indicated, it is obvious that a horizontal line 
through the frequency of one storm per year will indicate by its inter- 
sections with the various curves, the intensity which must be expected 
each year at the various intervals of time. It must also be noted that 




20 



30 40 50 60 70 80 
Interva/s of Time - Minutes 



90 



IOO I/O 



120 



Fig. 138. — Frequency of Intense Rainfalls at St. Paul, Minn, (see page 254). 

the intensity at the various intervals of time for any other term of years 
can be determined in the same way by the intersection of these curves by 
a horizontal line drawn through .a point below the frequency of one 
storm per year determined by dividing one by the number of years for 
which such curve is desired, as indicated in Fig. 138. Such curves de- 
termined for St. Paul are platted in Fig. 139, page 256. T These curves 
indicate a certain general progressive distribution which gives at least 



i This general method for determining frequency curves is that outlined by 
Metcalf and Eddy under the heading of "Frequency of Heavy Storms." They 
have also discussed "Intensity of Precipitation" at considerable length. See 
^'American Sewerage Practice," by Metcalf and Eddy, Vol. 1, pages 220 to 234. 



256 



Great Rainfalls. 



some indication of the probable frequency of the maximum curve first 
developed in Fig. 135, page 251. 

By platting interval curves in terms of intensity and years of occurr- 
ence as determined from Fig. 139 (see Fig. 140), and extending these 
curves beyond the limits of experience (shown by dotted lines), an es- 
timate can be made of the probable limiting time of the maximum 
curve which, as shown in Fig. 140, may be estimated as representing a. 




10 



zo so 



40 50 60 JO SO 
Infervaf-s of T/me - Minc/fes 



90 IOO 



//O 



IZO 



Fig. 139. 



-Intensity of Rainfall at St. Paul for- Various Frequencies (see 
page 255*). 



probable frequency of once in from 90 to 120 years. As previously 
noted, however, any attempt to extend actual experience beyond the 
term of years in which such experience is acquired is speculative and 
must be taken as indicative only and not as in any sense established. 

It is important that the engineer should also recognize the limiting 
value of the frequency investigation above outlined. With the present 
knowledge available, it furnishes perhaps the best basis for the study 
of this subject. Like the investigation of the annual rainfall at Boston, 
discussed in Sec. no, a similar investigation for a similar period of 
years in any given locality would doubtless give quite different con- 
clusions as to frequencies. 



Frequency. 



257 



It should also be noted that the rates of rainfall used in the investi- 
gation, especially for the longer intervals of time, are average rates and 
not uniform rates, and are therefore somewhat misleading when these 
longer intervals are considered. For example, the actual occurrence 
of the rainfall of August 8 and 9th, 1906, at Madison is shown in Fig. 
141 with the uniform rates of occurrence platted below and the average 




10 Mjpyl-^ 



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T 1 1 I 
Jo MW«p - 



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±*zi 



60_Mmufe_ Ra/nfa/J_ 



30 40 50 60 70, 8O 90 
Infervate of Occurrence - Ye<z?r&. 



WO I/O 120 



Fig. 140. — Expectancy of Maximum Rainfall Occurring at St. Paul. 

rates previously shown platted above. In the use of such data as a basis 
of engineering design, it is therefore essential that while taking all pos- 
sible advantage of the general methods of investigation above outlined,, 
the engineer should also study the actual manner of occurrence of max- 
imum storms which his designs must take into account. 8 

126. Approximate Maximum Intensities of Short Storms. — A 
brief study of intense rainfalls indicates that the limited time for which 
records are available at any one station is not long enough to give the 
maximum rates which are liable to occur at that station in the course of 
time. If the intensities at various stations in the same meteorological 



s Long Time New York Rainfall Records, by 0. Huf eland. Eng. News. 
Vol. 76, p. 450, Aug. 31, 1916. 
Hydrology — 17 



258 



Great Rainfalls. 



district are investigated, it is found that certain stations will show ex- 
treme conditions for certain intervals, while for other intervals extreme 
conditions are found to have occurred at other stations. For such dis- 
tricts there seems to be no reason why, in the lapse of time, storms of 



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Fig. 141.— The Intensity of Rainfall Occurring August 8, 1906, at Madison, 

Wis. (see page 253). 

similar intensity may not occur at any or all other stations in such dis- 
trict. If therefore the maximum rates of local rainfall at the various 
stations in a given district are determined for the period covered by the 
records, are then platted on one diagram, and a smooth enveloping 
curve is drawn through the maximum points shown by the local curves, 
such curves may be regarded as the maximum rate curve for the dis- 
trict, based on the combined experience of its local stations. Such a 
curve does not represent the extreme maximum which may occur, for 
such extreme conditions may never have been experienced at any of the 



Studies of Local Intensities. 259 

stations. Such a curve may perhaps be regarded as an experience 
curve of two or more times the length of the average record involved. 
It furnishes important limiting rates, the frequency of which cannot 
definitely be evaluated. It will be exceeded only at very rare intervals. 

In a study of the probable maximum rates of local rainfall for Wis- 
consin conditions, maximum rates of local rainfalls were investigated 
and curves of maximum intensity were made for various stations as 
shown in Fig. 142. From this diagram it will be noted that for intervals 
of 5 and 20 minutes, the intensities at St. Paul were maximum ; and for 
intervals of 10 and 15 minutes and for all other intervals from 30 to 
120 minutes, intensities at Madison were materially above those at any 
other station. The envelope ABCDE, therefore, seems to indicate the 
experience of extreme intensities for short duration for Wisconsin. 

In this same manner various studies have been made of the extreme 
local intensities at various points. 

127. Studies of Local Intensity. — One of the early studies of the 
intensity of local rainstorms was made by Professor A. N. Talbot 9 
in 189 1. Talbot platted all available records of local rainfall from all 
the stations in certain groups of states where he considered the condi- 
tions were similar, and drew certain curves to show the ordinary limits 
of "ordinary maximum rainfall" and of "rare rainfall." 

Fig. 143, page 261, shows Talbot's study of the rates of rainfall in 
the Northern Central States. The lower curve, which he terms "the 
curve of ordinary maximum rainfall" is represented by Equation 1 

1.75 

(1) i = 

T + .25 

The upper curve he terms "the curve of rare rainfall" which is rep- 
resented by Equation 2 



(2) 



• T + 0.5 

In these formulas i is the rate of rainfall in inches per hour for the 
time T expressed in hours. The points on the diagram represent the 
actual records of individual storms. It will be noted that the curve of 
rare rainfall has sometimes been exceeded. 

A number of attempts have been made to express mathematically the 
intensity of rainfall with respect to time. The results of some of the 



a Rates of Maximum Rainfall. A. N. Talbot. Technograph 1891-92, p. 103. 
See also Eng. News, July 21, 1892. 



260 



Great Rainfalls. 



i 

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Sf. Peru/ Minn. 



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O /O aO 30 <40 SO 60 70 8 90 /OO //O /20 
/Duration /n rrf/nufes 

Fig. 142. — Maximum Rates of Rainfall for Wisconsin Conditions (see page 259). 



Studies of Local Intensities. 



261 





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Fig. 143. — Talbot's Study of Maximum Rainfall Intensities of Short Duration 

(see page 259). 



investigations are given by the following formulas in which i is the rate 
of precipitation in inches per hour, and t is the duration of time ex- 
pressed in minutes : In this tabulation are also given the formulas of 
Prof. Talbot, reduced to similar units for comparison. 



262 Great Rainfalls. 



TABLE 28. 
Formulas for Maximum Rainfall. 
Formula Author Remarks 



105 



A. N. Talbot 10 Ordinary maximum 

A. N. Talbot Maximum occurring once 

in about 15 years 

A. N. Talbot Maximum exceeded 2 or 3 

times per century 

E. W. darken To be expected each year 

E. W. Clarke Exceeded once in 8 years 

E. W. Clarke Exceeded once in 15 years 

Kuichlingia 

Shermani-- (Chestnut Hill) . Maximum 

Sherman Ordinary 

C. E. Gregory Ordinary severe storm 

C. E. Gregory Winter storms 

C. E. Gregory Maximum 



io Rates of Maximum Rainfall. A. N. Talbot. The Teclmograph, 1891-2, 
page 103. Also, Rainfall and Runoff in Relation to Sewerage Problems. W. 
C. Parmley, Jour. Assoc. Eng. Soc, 1898. 

ii Storm Flows from City Areas, and Their Calculation. E. W. Clark. Eng. 
News, Vol. 48, p. 386. 

is Rainfall and Runoff in Storm Water Sewers. C. E. Gregory. Trans. Soc. 
C. E., Vol. 58, p. 458. Also, Maximum Rates of Rainfall at Boston. C. E. 
Sherman. Trans. Am. Soc. C. E., Vol. 54, p. 173. 



1. 


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180 


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to.087 




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Rainfall Formulas. 263 

Figure 144, page 264, shows a platting of a number of formulas to- 
gether with some curves for maximum rainfall rates which have been 
devised by various writers but which have not been reduced to a 
mathematical expression. 

The variation in the formulas and curves is due to the fact that they 
were derived from records of different localities and in some cases for 
quite different frequencies. In this figure, Curve 8 was constructed 
from the combined records of excessive rainfalls in the cities of Bos- 
ton, Providence, New York, Philadelphia and Washington and repre- 
sents the observations for an aggregate of about seventy years, and 
was the curve adopted by the engineers who made the report on the 
sewerage of the District of Columbia in 1890. 

An examination of the various curves shown in Fig. 144 will make 
it manifest that the application of any single formula to the determina- 
tion of probable local rainfall intensity is liable to lead to very errone- 
ous results, unless it is first determined whether or not the formula 
actually applies to the particular condition of the locality. In all cases 
where the problem to be solved is of importance, an independent inves- 
tigation should be made, or the origin and basis of the formula or in- 
tensity curve considered should be ascertained and its real application 
to the particular locality determined. 

128. Rainfall for Longer Periods. — Professor F. E. Turneaure has 
investigated the local rates of rainfalls that have occurred during 
longer periods and within certain general geographical boundaries, and 
has embodied the maximum results of his study in Fig. 145. Concern- 
ing the investigation on which this diagram was based, Turneaure 
says : 

"The records cover the period from 1871 to 1906, and all rainfalls 
are represented which exceeded in amount five inches in twenty- four 
hours, and, from 1894 to 1896, all those which equaled or exceeded 
two inches in one hour. As far as possible, the same storm is repre- 
sented but once for any one state, although records may have been re- 
ceived from several stations ; and furthermore each storm is counted 
as a one-day storm or a two-day storm, but not both. A one-day storm 
is one in which all the rain falls in a meteorological day, that is, from 
8 P. M. to 8 P. M., and in a two-day storm, all the rain falls within 
two such days. A one-day storm may therefore have fallen in a few 
hours, and likewise a two-day storm, so that the figures given do not 
necessarily represent the maximum rates. However, by taking the' 
maximum from among a great many records the figures thus found 



264 



Great Rainfalls. 




60 90 /20 

t = T//7?e /n tf?//7u/es. 



/80 



Fig. 144. — Intensity Curves for Storms of Short Duration (see page 263). 



Local Rainfall Intensity. 



265 



for the one and two-day storms will approximate the maximum for 
twenty- four and forty-eight hours. The one-hour rates are well de- 
termined. The number of times a rainfall has exceeded the given 
amounts is an indication of the frequency of heavy storms and also to 
some extent, of the reasonableness and reliability of the maximum fig- 
ure. Those states having the highest maximum rates are those where 
heavy rainfalls are the most frequent. 



24 
































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8 16 24 32 40 43 

Dura //on of /-?o/n/a// Hours 

Fig. 145. — Turneaure's Curve of Local Rainfall 
Intensities (see page 263). 

"The curve for the Northern and Central States is somewhat ex- 
ceeded in a few states, but for most of them it represents rainfalls but 
little greater than those which have already been observed and which 
may occur again at any time. The curve for the South Atlantic and 
Gulf States represents the maximum recorded rainfalls for all the 
states of this group except Louisiana, for which the records far exceed 
those of any other state." 13 

To the original figure have been added the rainfall at Cambridge, 
Ohio, July 16, 19 14, and at Altapass, North Carolina, for the maximum 
twenty-four hours of July 15-16, 1916, and a few other records of ex- 
treme rainfalls. As noted from the above quotation, the curves were 
not drawn to show extreme maximums but rather the probable maxi- 



13 Public Water Supplies. Turneaure and Russell. 2d Ed., p. 49 et seq. 
See ak:o Table 7 for detailed study on which diagrams were based. 



266 Great Rainfalls. 

mums for perhaps a twenty-five year period. The added data show 
that to include extreme intensities, the curves would all probably have 
to be raised considerably and that even for a twenty-five year period 
they might have to be altered somewhat in the light of the twenty 
years of observations which have elapsed since the end of the period 
on which the curves are based. 

129. Intensity Over Large Areas.- — The local intensity of rainfall 
which has been previously considered is that determined from single 
stations or groups of stations and is therefore applicable only to limited 
areas. Such intense rains never extend over large areas, and the esti- 
mates based on such observations cannot be applied to any consider- 
able drainage areas. It is to be noted, however, that it is by no means 
certain that the maximum intensity recorded by a given gage in a cer- 
tain area represents the maximum intensity of rainfall that has oc- 
curred on that area, and indeed it is probable that the records in prac- 
tically all cases are actually below the maximum that has occurred as 
the gage area is such a small part of the area which any storm covers. 
This fact somewhat offsets the error in the application of the data to 
areas of considerably greater size, which would not be warranted other- 
wise. 

In the consideration of the flood flows of streams and the maximum 
discharge of considerable drainage areas, the factors of both intensi- 
ties and area become important, and the engineer must again have re- 
course to the records of the Weather Bureau. 

In the great storms of March 24-27, 1913, which were the main 
cause of the flood of the same dates, the ground over most of the re- 
gions where floods occurred had previously been saturated by the 
storm of March 20-23, 1913, which has been illustrated in Fig. 31, 
page 70. This storm was almost immediately followed by the storm 
of March 24-27 although there was a sufficient cessation of rain to 
make the two storms entirely distinct. The extent of the storm 
of March 24-27 for each of the days included is shown by Fig. 146, 
page 267, and its distribution of intensity over the area particularly af- 
fected by the floods is shown in Fig. 147, page 268. By measuring 
the areas surrounded by the various isohyetal lines, the distribution of 
the rainfall of this storm for different intensities can be approximately 
determined ; and by a similar measurement of similar maps drawn to 
show the distribution of the maximum rainfall for one. two and three 
days, similar data can be approximately determined for such periods. 

Figure 148. page 268, shows curves for the distribution of intensity 



Intensity over Large Areas. 



267 










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268 



Great Rainfalls. 




Fig. 147.— Depth of Rainfall, March 24-27, 1913 (see page 266). 




/O 20 30 40 50 60 70 60 90 /OO 

Area Covered /'r? Thoasa/r?c/s of Square A7//e3. 

Fig. 148. — Rainfall Intensity for One to Five Days (see page 266). 



Extent of Storms. 



269 



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270 



Great Rainfalls. 



of this storm for periods of one, two, three, four and five days. 14 In 
the investigation of the problem of the maximum storms which might 
possibly visit this area, it was soon ascertained that a storm on essen- 
tially the same path had occurred in October, 1910, but that the most 
intense rainfall had occurred westerly from the center of the area of 
intense precipitation of the storm of March, 1913. 



'Y^onsas dry 




Fig. 150. — Isohyetal Lines for Storm of October 4-7, 1910. 

The path and geographical extent of the storm of October, 19 10, is 
shown in Fig. 149, page 269, and the isohyetal lines are shown in 
Fig. 150. 

130. Excessive Rainfall of the Eastern United States. — After the 
great flood of March, 19 13, an investigation of both rainfall and flood 
records was undertaken by the Miami Conservancy District in order 
to determine whether the flood that had just occurred might be re- 
garded as the maximum that might ever be expected or whether the 
flood protective work should be designed for a flood of greater magni- 
tude. This work, which was undertaken by the Morgan Engineering 
Company under the direction of Mr. A. E. Morgan, Chief Engineer, 
is believed to be the most complete and thorough investigation of the 
problem of the intensity of rainfall over extended areas that has ever 



14 From data furnished by A. E. Morgan, Chief Engineer Miami Conserv- 
ancy District. 



Excessive Rainfall. 271 

-been attempted. While the research was undertaken with special re- 
gard to Ohio and the adjacent country, it covered quite thoroughly the 
eastern half of the United States and will furnish a basis for reliable 
estimates over this entire area. As a basis for this study, the rainfall 
records were abstracted for all storms in the United States east of the 
103 ° of longitude, including all rainfalls that equaled or exceeded the 
following limits : 

For stations where normal annual rainfall exceeded twenty inches, 
all storms where the total rainfall for a single day equaled 10 per cent 
or the total rainfall for the entire storm equalled 15 per cent of the 
normal annual rainfall. 

For stations where normal annual rainfall was below twenty inches, 
-all storms of one inch in twenty-four hours or four inches for the total 
storm. 

The investigation included some 3,000 stations. Some of the most 
valuable results of these studies relative to local rainfalls are embodied 
in six maps showing the maximum rainfalls in each of the quadrangles 
in one to six days. 15 These maps have been summarized in Figs. 151 
and 152, pages 272 and 273. In Fig. 151 the maximum rainfalls for 1, 2 
and 3 days are shown in each quadrangle, and in Fig. 152 the maximum 
rainfalls for 4, 5 and 6 days are also shown. These maps include only 
data available to Dec. 31, 1914, and for stations having rainfall records 
for five years or more. These investigations include 2641 storms. Of 
■these 1,236 were found to be storms registered at only single sta- 
tions and therefore of no great geographical extent. Nine hundred 
-and ninety-six storms were recorded at from two to five stations, and 
409 storms were recorded at more than six stations. For the purpose 
of the investigation, only storms that covered 500 square miles or 
more and that had a total precipitation of at least 20 per cent of the 
normal annual rainfall were studied in detail. Of seventy-eight such 
storms, the twenty-seven largest were chosen for final consideration. 
The geographical location of these storms as shown by the limiting 
isohyetal lines of five inches of rainfall is given in Fig. 153, page 274. 

131. The Application of Data. — In considering the rainfall data 
available from areas widely separated geographically, and conse- 
quently greatly differing in climatological conditions, it is important to 
determine what data may be regarded as applicable to local conditions. 

It has already been pointed out that local rainfall is induced by cer- 



15 Storm Rainfall of Eastern United States, by the Engineering Staff of 
the District. Technical Reports, Part V. The Miami Conservancy District, 
Dayton, Ohio, 1917. 



272 



Great Rainfalls. 



tain conditions among which the most important are the directions, 
paths and intensities of the storms to which the locality is subjected 
and its situation relative to the sources of moisture from which the 
rainfall must be derived. While storms of great intensity occur far 




18" I7~~ 16" /5 
Fig. 151. — Maximum Depths of One, Two and Three Day Rainfalls. 

from the location of areas of maximum evaporation, it is evident that 
such distances limit to a considerable extent, the frequency of occur- 
rence, the duration of high intensities the extent of area over which 
such intensities may occur, and the maximum intensities to which such 
localities may be subject. While the storms of July, 1914, in Ohio (see 
Sec. 121) and of July, 191 2, in Wisconsin (see Sec. 123) are equal to 
many similar storms which have occurred in the Gulf and South Atlantic 
States, it is believed that such storms are approximating a maximum, for 
those localities, and that no such storms as those which occurred in the 
Carolinas in July, 1916, in Porto Rico on August 5-9, 1889, or at Mont- 



Excessive Rainfall. 



273 



erey, Mexico on August 25-29, 1909, are physically possible in Wiscon- 
sin, Ohio or other regions similarly located. 

It is also important to note that the greatest local or general 
storms are likely to occur during seasons when evaporation and con- 



18 /7 /6 /5 M 13 12 II 10 9 L 
103' /Or 99' 97' 95' 93' 91' 89' 87' 85' 83' 



7 6 5 4 3 2 I 
?/• 19' 77" 75' 73' 71' 69' 67' 




103- f8 ^ /7 39- l6 SY J5 35 /4 93' /3 9r /2 89' // 87' /0 85' 9 83' Bf 



7 79 ' 6 ir 



Fig. 152.— Maximum Depths of Four, Five and Six Day Rainfalls. 

sequently atmospheric moisture is' at a maximum, that such conditions 
appear essential to their occurrence, and that in consequence it is im- 
probable that even such excessive storms as are known to occur can 
occur during cold periods, especially in the north when the ground is 
covered by a deposit of snow. 

While a storm similar in intensities to the great storm of October, 
19 10, must be anticipated as a future possibility at other localities in 
the country adjacent to its path, it is unlikely that such a storm will 
occur during the early spring under conditions of materially lower tem- 
perature. It is not therefore to be anticipated for any given locality 
Hydrology — 18 



274 



Great Rainfalls. 



that with the lapse of time, storms are bound to occur which will be 
equal to any other storms which may have occurred in any other lo- 
cality. For each particular locality there are undoubtedly limits which 
it is physically impossible that rainfall can exceed in intensity, dura- 
tion and extent. What those limits may be cannot be determined with 




Fig. 153. — Limit of 5-inch Isohyetals of Great Storms of Eastern United 
I States. 

any great degree of exactness on account of the short time for which 
rainfall records are available, but the observations of the flow of streams 
in other countries for many centuries, bear out the conclusion that such 
limits do exist and that they can be approximately determined. 

When such flood records are available for hundreds of years, the 
flood heights of the several greatest floods agree within a few feet of 
each other, and in such long time records no one flood is found to 
greatly exceed other extreme floods. The greatest flood that occurs 
once in a thousand years does not greatly exceed the maximum flood of 
one hundred or even of fifty years. It is reasonable to assume that the 



Frequency of Storms. 275 

great rainfalls, which are the principal underlying cause of the floods, 
will not in the lapse of centuries vary to a much greater degree than 
the floods they produce. 

132. Frequency of Storms of Various Magnitudes. — In the studies 
of maximum rainfall undertaken by the Morgan Engineering Com- 
pany for the Miami Conservancy District, the country east of the 103 
meridian was divided into districts on the odd degrees, thus giving 133 
two-degree quadrangles. (See Figs. 151 and 152, pages 272 and 273.) 
To determine the frequency of storms of various magnitudes as well as 
the maximum storm which might be expected to occur within a given 
period of time in each quadrangle, 16 the years of record for each of the 
several stations within each quadrangle were totaled, as were also the oc- 
currence of storms of a given intensity. By dividing the total year of ex- 
perience in the quadrangle by the number of storms of the given inten- 
sity, the time interval was estimated for that particular storm intensity. 
By repeating this process for storms of various intensities, estimates 
were made for which frequency curves for each quadrangle were con- 
structed. The quadrangle which includes the Maimi River is shown on 
Fig. 154, page 276, and the frequency curves for this quadrangle, based 
on estimates made as above described, are also shown in the same figure. 
From these curves the frequency of the maximum storm intensity for 
one or more days within the experience of the Miami quadrangle can 
be estimated, and the probabilities of greater storms within terms of 
years beyond the experience of the area can be approximated by their 
extension. It will be noted that the general form of the curves is simi- 
lar to and vertified by the local intensity curves previously shown in 
Fig. 134, page 249. 

In order to compute the intensity of a storm that will probably occur 
once on an average of 50 or 100 years, the sum of the record years of 
all stations in each quadrangle was divided by the number of years in 
the period considered. For example : if a total of 360 storm years 
were on record in a given quadrangle, the average maximum storm for 
a 50 year period would be the average of the seven (7.2) maximum 
storms experienced, and for a 100 year period the average of the 
four (3.6) maximum storms experienced. For this purpose no sta- 
tion with a record of less than 10 years was considered. 

The results of these studies are embodied in some 24 "Isopluvial" 
charts for 15-year, 25 year, 50 year and 100 year periods, and for 1, 2, 
3, 4, 5 and 6 days rainfall for each period, all constructed on the above 



16 Eng. News, Vol. 77, p. 15. 



276 



Great Rainfalls. 



principle. 17 Maps so constructed are perhaps reasonably indicative of 
conditions which may be expected to obtain. They represent an attempt 
to analyze a most complicated subject by using such data as are now 




30 AO 50 60 

^reepuency, rears 
Fig. 154.— Intensity Studies for Miami Quadrangle ie (see page 275). 

available but which are admittedly insufficient for drawing definite con- 
clusions. 

The reliability of this method of investigation for determining the fre- 

i" Storm Rainfall of Eastern United States. Technical Reports, part V. 
Miami Conservancy District, 1917. 



Frequency of Storms. 277 

quency of maximum rainfall occurrences depends at least partially upon 
the actual occurrence of the maximum extreme conditions within the ex- 
perience of some of the stations within the quadangle or district consid- 
ered. If the occurrence of rainfalls of great magnitude is of a periodic 
character for correct results the period of maximum intensities must be 
included in the record, and if occasional exceptional conditions will 
occur at very rare intervals, they will not be discovered unless very 
long records are available. 

This method while an interesting basis of investigation, cannot be 
regarded as strictly correct for if correct it should be possible to obtain 
300 years of experience from 300 one-year observations at 300 separate 
stations within a single quadrangle. It is evident that as all such 
limited areas must be subject to similar meteorologic conditions, an 
exceedingly dry or an exceedingly wet period would affect all of the 
stations and thus give erroneous conclusions. It is evident that the 
occurrances at any station in a district having similar meterological con- 
ditions may be taken as a fair criterion of what may occur at other sta- 
tions in that district ; but the extreme occurrences at any one station will 
not fairly represent the extreme which may occur at any one station 
during a period equal to the sum of all the periods for which observa- 
tions have been taken at all the stations in the district. 

133. Time-Area-Depth Curves for Major Storms. — In the investi- 
gations of the Miami Conservancy District, ls the study of major 
storms included among others the nine major storms listed in Table 29. 

TABLE 29. 

Major Storms Considered l>y the Engineers of the Miama Conservancy Dis- 
trict as Applicable Thereto. 
Index Date Center of Storms 

a May 31-June 1, 1889 Pennsylvania 

b Julyl4-16, 1900 Iowa 

c Aug. 26-28, 1903 Iowa 

d June 9-10, 1905 ". Iowa 

e July 5-8, 1909 Kansas 

f July 19-22, 1909 Michigan 

g Oct. 4-6, 1910 Southern Illinois 

h March 23-27, 1913 Ohio 

i August 17-20, 1915 Arkansas 

The time-area-depth curves of these storms for one, two and three 
day periods are shown in Figs. 155, 156, and 157, pages 278 and 279. 

It should be noted that all of these storms, with the exception of that 
which actually produced the great flood in the Miami Valley, occurred 

is Report of Chief Engineer, Miami Conservancy District, Vol. I, p. 87 et seq. 



278 



Great Rainfalls. 



late in the season and it is improbable that storms equal to the three 
maximum will ever occur in the Miami Valley early in the season with 
frozen or snow covered ground. 



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Fig. 155. — Time-Area-Depth Curve for 24-Hour Storm. 



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Fig. 156. — Time-Area-Depth Curve for 48-Hour Storm. 

Nevertheless the uncertainties involved warrant the use of adequate 
factors of safety in all designs involving the safety of life and prop- 
erty. 

134. The Study of Extreme Conditions of Rainfall. — In estimat- 
ing extreme conditions additional light can be obtained by examining 
the extremes at other stations within a district having similar meteoro- 
logic conditions and basing maximum and minimum estimates on limits 



Stucfy of Extreme Conditions. 



279 



fixed by similar occurrences within the district ; but the frequency with 
which such events are likely to recur can at best be but roughly esti- 
mated. The extreme conditions of the one day rainfall for quadrangle 
B-12 in northern Wisconsin, shown in Fig. 151, are largely fortuitous 
and are scarcely liable to recur at the same locality in perhaps the next 
one hundred years or more but are liable to occur at any time at some 
other point within Wisconsin or in adjacent states. In the same way 
the extreme intensities of the storm of June, 1889, at Alexandria, Louis- 
iana, shown in quadrangle L-13 will scarcely be expected to obtain 



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0/Z3456789/0 
Storm fireo in Thousands of Square M/'/es 

Fig. 157. — Time-Area-Depth Curve for 72-Hour Storm (see page 277). 

again at this locality for many years ; but it seems quite probable that a 
similar storm may occur at any time within the Southern States as did 
the storm of July, 191 6, in the Carolinas which, had it occurred at the 
time of the construction of these maps, would have materially modified 
the intensities shown for the quadrangle G-8. The maximum depart- 
ure from the mean annual rainfall at Madison is -f- 21.3" and — 18.14". 
It seems quite possible that any station in Wisconsin may experience 
departures of equal magnitude, but the combination of all the station 
experience in the State would not give the frequency of occurrences 
that the sum of those observations represent, and would lead to a false 
idea of the meaning of the data. 

The extraordinary rainfall of August 8-9, 1906, at Madison, Wis- 
consin, was found to be the storm of maximum intensity for periods of 
from 30 to 120 minutes for stations in and adjoining the State of Wis- 
consin, as shown in Fig. 142, page 260. It is evident that the frequency 
at which such a storm must be expected to occur in any locality in Wis- 



280 Great Rainfalls. 

consin cannot be definitely or even approximately evaluated with the 
limited records available. The combined time of record shown in Fig. 
142 is 183 years, but in comparison with the estimated length of the 
maximum experience at St. Paul (Section 125) , this would be too low an 
estimate of frequency for the Madison storm. 

The necessity of long time records to cover extreme variations in 
annual rainfall is illustrated by the curve of progressive means for 
Southeastern New England (see Fig. 117, p. 211). This curve is 
below the mean for 26 years from 1833 to 1858 inclusive, and there are 
52 years between its minimum in 1837 and its maximum in 1889. It 
is probable that frequency determination and intensity-duration-depth 
maxima, even when considered for extended areas, may require a sim- 
ilar or even a greater time for their full appreciation. It seems prob- 
able therefore that the average length of record of the various stations 
for which observations are available especially in many parts of the 
area covered by Figs. 151 and 152, is not sufficient to fully cover the 
long time probabilities, and that in some cases the occurrence of un- 
usual and rare storms, on account of the time limitations of the data 
available, unduly accentuate the occurrence of intensities in certain dis- 
tricts and underrate the probabilities of similar occurrence in other dis- 
tricts. 

135. General Conclusions. — It is important that all should recognize 
our unfortunate but necessary ignorance of the frequency with which 
such extraordinary events obtain, and that we are entirely unable to for- 
mulate any exact rules for such occurrences. In many cases the con- 
trolling element of cost will not permit works to be designed to care for 
such unusual conditions, and in cases where property loss alone is to be 
considered and where no loss of life is uivolved, the extreme conditions 
must be ignored in the design with the understanding that occasional 
loss is more desirable than unwarranted expense. Deductions that can 
be drawn from extended studies on lines similar to those above dis- 
cussed, especially when the studies apply to the older parts of the coun- 
try where considerable data are available, are believed to furnish an 
adequate basis for- engineering design. Such uncertainties as remain 
must be covered by adequate factors of safety. 

LITERATURE. 

Excessive Rainfall. Eng. News, 1S94, "Vol. 31, p. 409. 

Rate of Precipitation, Ithaca, N. F., J. H. Fuertes. Eng. News, 1894, Vol. 32, 

p. 22G. 
Maximum Rates at Boston, D. Fitzgerald. Eng. News, Vol. 11, May 31, 1884. 



Literature. 28 1 

Excessive Rainfall in Neio York City, 1S99-1905, C. H. Nordell. Eng. News, 

1909, Vol. 61, p. 265. 
Maximum Rainfalls at Mobile. Ala, 1872-1891. Eng. News, 1901, Vol. 46, p. 26. 
Record of Rainfall of the American Continent at Jewell, Md., July 26 and 27, 

1897, Kenneth Allen. Eng. News, 1902, Vol. 48, p. 190. 
Report on Floods of May and June, 1901, E. W. Myers. Eng. News, 1902, Vol. 

48, p. 102. 
Maximum Rates of Rainfall at Boston, C. E. Sherman. Trans. Am. Soc. C. E., 

Vol. 54, 1905, p. 173. 
Record Heavy Rainfall at Sidney, N. S. W., C. H. Wilcox. Eng. News, 1910, 

Vol. 83, p. 171. 
Remarkable Fall of Rain in Arizona and Sari Diego. Eng. News, 1898, Vol. 

39, p. 298. 
Rainfall and Runoff in Relation to Sewerage Problems. W. C. Parmlee. Jour. 

of Assoc. Eng. Soc, 189S. 
Storm Flows from City Areas and Their Calculation, E. W. Clarke. Eng. 

News, Nov. 6, 1902, Vol. 48, p. 386. 
Rainfall and Runoff in Storm Water Seioers, Chas. E. Gregory. Trans. Am. 

Soc. C. E., Vol. 58, p. 458, June, 1907. 
Variations in Precipitation as Affecting Water Works Engineering, C. P. Bir- 

kinbine. Jour. Am. W. W. Asso., Vol. 3, 1916, p. 1. 
The Relation of Rainfall to Mountains, W. H. Alexander. Monthly Weather 

Review, 1901, p. 6. 
The Theory of the Formation of Precipitation on Mountain Slopes, Prof-. F. 

Pockels. Monthly Weather Review, 1901, p. 152. 
See also Mechanics of the Earth's Atmosphere, Smithsonian Miscellaneous 

Collection, Vol. 51, No. 4, Article VIII. 
Effects of Mountains on Humidity , Cloudiness and Precipitation, Dr. Julius 

Hann. Handbook of Climatology, translated by R. De C. Ward. The 

MacMillan Co., New York, 1903. 
Rainfall in England in Relation to Altitude, W. Marriott. Quar. Jour. Royal 

Met. Soc, Vol. 26, 1900, p. 273. 
Phenomenal Rains the Cause of Southern Floods. Eng. News, Vol. 75, 1916, 

p. 183. 
Long-Time New York Rainfall as the Basis for Sewer Design, O. Hufeland. 

Eng. Rec, Vol. 76, 1916, p. 393. 
Southern Rains \<ind Floods of July. 1916, Exhibited. Eng. News, Vol. 76, 

1916, p. 886. 
The Remarkable Rainfall of Oct, 1, 1913, Neiv York City. Eng. News, Vol. 70, 

1913, p. 887. 
Winnipeg Rainfall, F. Hill Parr, Can. Engr., Vol. 25, 1913, p. 4S7. 
Twelve Inches of Rain in Twelve Hours at Galveston, A. T. Dickey. Eng. 

News, Vol. 70, 1913, p. 945. 
Southern California Flooded, E. R. Bowen. Eng. News, Vol. 69, 1914, p. 123. 
Some Heavy Rainfall, K. Allen. Eng. News, Vol. 76, 1916, p. 1001. 
Extraordinary Rain in St. Louis toith Study of Runoff, W. W. Horner. Eng. 

News, Vol. 74, 1915, p. 742. 



282 Great Rainfalls. 

Excessive Rainfall at Galveston, Tex., 1898-1913, A. T. Dickey. Eng. News, 

Vol. 71, 1914, p. 69. 
Intensity of Rainfall Studied at Columbus, 0., Chas Herrick. Eng. News, 

Vol. 74, 1915, p. 678. 
Surface Water Supply of Hawaii, N. C. Grover, U. S. G. S. Water Supply 

Papers, No. 430 and 445, 1917. 
Storm Rainfall of Eastern United States, Engineering Staff of the District, 

Technical Reports, part V. The Miami Conservancy District, Dayton, 

Ohio, 1917. 
The Miami Yalley Flood Protection Work. Eng. News, Vol. 77, 1917, p. 12. 
Tropical Rains — Their Duration, Frequency and Intensity, Oliver L. Fassig. 

Mon. Weath. Rev., June, 1916, p. 329. 



CHAPTER XII 
RAINFALL AND ALTITUDE 

136. Importance of Subject. — A brief discussion of the relations 
of altitude and precipitation has been presented in Sec. 87, but 
the importance of the subject is such that a more detailed consideration 
seems desirable. The fact that in many cases precipitation increases 
with altitude is well known, but the further fact that this condition is 
not universal and that such increase, if any, is sometimes obscured or 
even reversed by the influence of the geographical location with ref- 
erence to sources of moisture and storm paths and by topographical 
relations is not always understood or appreciated. Attempts must oc- 
casionally be made to estimate the quantity of a water supply which 
may be expected from a mountain drainage area on the basis of the 
known rainfall at valley stations, for which alone data are usually 
available. In some cases the data are sufficiently complete and the 
conditions sufficiently well known to warrant the assumption that the 
mountain rainfall will exceed the valley rainfall, and a fairly positive 
estimate is possible of the probable effect of altitude on the average 
rainfall conditions on the drainage area which is under investigation. 
Such estimates, however, are sometimes made on insufficient data or 
on a basis that is found to obtain at other localities where conditions 
may be widely different. Unless estimates are made with great care 
and based on sufficient pertinent data, they are likely to be seriously in 
error and to be followed by disastrous results. Sometimes the de- 
sire for a sufficient water supply rather than a careful consideration of 
the physical conditions modifies the estimates, and works that are con- 
structed on such unfound assumptions must usually result in failures 
more or less complete. 

The study of such problems in almost every case is greatly compli- 
cated by the lack of rainfall stations in the mountains. Compara- 
tively few such stations exist, and information covering many areas 
is entirely lacking. In. other cases, where a few such stations are es- 
tablished, the data are more or less incomplete and misleading for the 
detailed distribution of rainfall in the mountains is more uncertain 
than in the country having more uniform topography on account of 
the fact that the irregular topography of the mountains greatly affects 
the distribution of the quantity of precipitation and the variations from 
point to point in adjacent territory are very irregular. 



284 Rainfall and Altitude. 

Several attempts have been made to express the relations of altitude 
and rainfall by rules or formulas (see Sec. 143), and however com- 
mendable such work may be when limited in application to local con- 
ditions, such rules are exceedingly misleading when an attempt is made 
by the uninformed to apply them to general use. For these reasons a 
study of the subject in some detail seems desirable and a still more 
detailed study of local conditions is essential when a working estimate 
is to be made for any important purpose. 

137. General Considerations. — The greatest annual rainfall usually 
occurs where moist winds are forced to rise in passing over mountains, 
causing dynamic cooling and consequent precipitation. Such condi- 
tions more especially obtain where mountains rise abruptly from the 
sea and are located in general at right angles to prevailing storm move- 
ments, as is the case on the North Pacific Coast of North America (see 
Fig. 109, page 201), the west coast of Scotland, Norway, Dalmatia, 
India, Japan and numerous other similar locations. Similar conditions 
also obtain on mountains at some distances inland where extreme rain- 
fall conditions are occasioned by winds of exceptional intensity such 
as the hurricane winds that produce the heavy precipitation on the 
Southern Appalachians in North Carolina (see Fig. 96, page 175), and 
the monsoon winds (see Fig. 24, page 61) that produce the excessive 
precipitation on the Himalayas of Northern India. These conditions 
not only increase the rainfall on the windward side of the mountains 
and to some extent on the low lands to windward, but also compara- 
tively decrease the rainfall to some distance to the leeward of the 
mountains. As the winds pass over the divide, their absolute humidity 
having been decreased by the induced rainfall, they are compressed in 
their flow down the mountain, and in consequence become dry winds. 
In some cases after such reduction in rainfall has occurred, heavy 
precipitation again results from higher ranges of mountains farther in- 
land. This is shown by the conditions in California, illustrated by 
Fig. 91, page 170. The low coast range which rises abruptly from the 
Pacific Coast induces an average annual precipitation of about 60 
inches, producing also a comparative reduction of the annual rainfall 
to 40 inches and less on the contiguous inner ranges and to 20 inches 
and less on the interior valley. In ascending the Sierra range the 
rainfall again increases to an average of 40 inches and over, decreas- 
ing again in the mountains and valleys beyond. In India the South 
West monsoons (see Fig. 24, page 61) first encounter the Western 
Ghauts (elevation 5,000 to 6,000 feet) which induce a rainfall of from 
80 to 160 inches. Beyond these mountains there is a reduction in pre- 



General Considerations. 285 

cipitation to about 20 inches which again gradually increases to 40 
inches or more in the interior, reaching the heaviest precipitation en- 
countered any where in the world at certain stations in the Himalayas 
(see Table 2.7, page 248). The rainfall in the Himalayas is said to de- 
crease above 5,000 feet, to fall to about 30 inches near their top and 
to 10 inches and less in the interior plains of Tibet. 

In Norway the annual rainfall is 88.70 inches at Bergen, 145.15 
inches at Seathwart in the mountains, and 189.43 inches at Sty-head 
pass (elev. 1,600 feet), while at Christiania on the lee of the mountains 
it is 21.18 inches. 

The mountains having the greatest rainfall in Germany are the Was- 
genwald and the Schwarzwald. The following table shows how the 
rainfall increases with the altitude, taken in the Thur Valley of the 
Southern Vogesen Mountains in the year 1880. 

TABLE 30. 
Rainfall in the Vogesen Mountains. 

Altitude Rainfall 

Station Feet Inches 

Sennheim 900 32.28 

Thann 1,100 38.19 

Weiler 1,260 55.90 

St. Amarin 1,320 59.06 

Wesserling 1,400 64.18 

Odern 1,510 75.98 

Wildenstein 1,870 99.21 

In similar manner, Osterode in the Harz Mountains has 31.30 inches 
of rainfall, while only seven miles away at Klausthal, 1,160 feet high, 
on the rainy side of the mountains, the rainfall is 58.70 inches. 

In many cases diagrams platted to show the relation of altitude tO' 
rainfall for certain valleys or topographical districts (see Fig. 158,. 
page 286) indicate a marked increase in rainfall with altitude, and with 
selected stations the relation is frequently so definite as to give con- 
fidence in the possibility of the establishment of dependable rules for 
such relations as applied to local conditions. As more stations are 
added to the diagram, considerable exceptions are found to exist and 
any rule so established is seen to be liable to serious error unless to- 
pographical relations are considered, and even such considerations will 
with our present knowledge be inadequate to explain all of the dis- 
crepancies. 

This diagram shows an interesting feature in the continually dimin- 
ishing rates of the increase of rainfall with altitude as the river val- 
leys considered become more and more shut off from the ocean. The 



286 



Rainfall and Altitude. 



rate of increase of rainfall with altitude as shown by the slope of the 
lines on the platted diagrams depends upon the absolute humidity. 
In this diagram the flattest line shows the greatest rate of increase of 



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Fig. 158. — Variation of Rainfall with Altitude in Certain Valleys in North- 
western United States (see page 285). 

rainfall with altitude and is for an area near the coast, and it should 
be noted that the slope of these lines increases and the rate of rainfall 
increase continually gets less and less as the river valleys considered 
are farther inland and the moisture content is reduced by precipita- 
tion. This tendency is exhibited by all the diagrams and shows uni- 
formly greater rates of rainfall increase with altitude in those valleys 



General Considerations. 



287 



situated so that they receive air of greater absolute humidity. Another 
point to be noted is that the more broken and irregular the topography, 
the greater is the difficulty of determining any fixed relation between 
altitude and rainfall; this is shown on the diagram by the greater 
scattering of the plotted points. This probably is due entirely to the 
effect of the various topographic features in influencing the direction 
and moisture content of the prevailing winds. 



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Average Annua/ Pa/rtfa//, /ncnes. 

Fig. 159. — Variation of Rainfall with Alti- 
tude in the Region of Mount Washing- 
ton. 

A cursory examination of a topographical map on which isohyetals 
have been drawn will give the idea that such isohyetals fairly well de- 
fine the topography of the country and demonstrate a fairly constant 
relation between altitude and rainfall, at least when places on either 
the windward or leeward side of the mountains are considered by 
themselves. A more detailed study of the conditions that obtain, how- 
ever, will show that this apparent demonstration of a general law is 
largely due to the method necessarily used for drawing isohyetals with 
only limited data available and that the apparent uniformity of increase 
of rainfall with altitude is more imaginary than real. For example, Fig. 
159, page 287, shows the relations that actually obtain between the 
average annual rainfall and the altitude of various rainfall stations in 
the New England States between the sea and the top of Mount Wash- 



288 



Rainfall and Altitude. 



J"X 



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% » A7f. Wosntnqfon -£/. 6Z93 ft., &k: tfnn. ea/nra// 85.53 Inches. 



Fig. 160. — Average Rainfall of the New England States Showing Relation, 
to Altitude and Geographical Location (see page 290). 



General Considerations. 289 

ington. The map of this region (Fig. 160, page 288) will apparently 
show a somewhat constant increase of rainfall toward the summit of 
the mountain. If, however, we examine Fig. 159, we find that of the 
sixteen stations shown on the map between Mount Washington and 
the seas, all are below elevation 800 feet, and that Mount Washington 
has an elevation of about 6,200 feet. The annual rainfall of the sta- 
tion near sea level varies from about 35 to 46 inches and averages 
about 41 inches, while the average annual rainfall of Mount Wash- 
ington is over 85 inches. With such an indefinite starting point and 
no stations between 800 and 6,200 feet, the direction of the gradient 
of rainfall intensity is not well established, and the dotted lines indi- 
cate gradients which may possibly obtain. It is evident that for sta- 
tions between 2,000 feet and 5,500 feet, estimates of average annual 
rainfall may vary 10 to 25 inches or more from the truth, and that 
such estimates can not be made with any great degree of accuracy. 

138. Factors Affecting Amount of Precipitation. — It has been 
shown that the intensity of rainfall is influenced by location rela- 
tive to (a) sources of moisture and direction of normal winds, 
(b) paths of cyclonic storms, and (c) the topographical relief of the 
country. Mountainous countries by causing an upward flow of moist 
atmospheric currents produce expansion, dynamic cooling and conse- 
quent precipitation. Topographical relief is only one element in the 
problem ; before precipitation will occur there must also be moist at- 
mospheric currents, moving in such a direction that they will rise and 
expand sufficiently to produce relative humidities at and below the 
dew point." 

The presence of moisture is more essential to precipitation than high 
altitudes. For example, the Pacific Coast Range of the United States, 
with an elevation of about 3,000 feet, induces a precipitation of 60 
inches or more from the currents of moist air from the Pacific Ocean, 
while the higher altitudes of the Sierras (9,000 to 11,000 feet) induce 
a materially less rainfall from the air currents which have been con- 
siderably reduced in their absolute humidity (see Fig. 91, page 170). 
While the general drift of the atmosphere in the United States is east- 
erly, it has also been shown that in general the local air currents are 
toward the centers of low pressure, and continually vary with the prog- 
ress of the storm center. Thus in turn each source of moisture in or 
adjacent to the continent is induced to contribute more or less vapor to 
the atmosphere and to the precipitation induced by the passage of 
storms. 

Hydrology — 19 



290 Rainfall and Altitude. 

The study of almost any rainfall map will show many anomalies 
which cannot be satisfactorily explained. The paths of storm centers 
while approximately constant vary from year to year and from storm 
to storm. The intensities of the centers vary and the directions of the 
consequent incoming air currents are subject to many contingencies that 
are entirely fortuitous so far as human understanding is concerned. 
The consequent rainfalls are never the same for any two storms and still 
less similar for any combination of storms. This will be clearly ap- 
preciated from a study of the annual rainfall maps of Wisconsin 
(pages 205 to 206) an area in which the topographical relief is so 
small as to have little or no influence on precipitation. In the same 
manner that the varying storm intensity and movement combine with 
the sources of moisture and geographical location to produce changes 
in the distribution of precipitation, so the same factors combine with 
altitude to produce varying conditions at elevated stations and as the 
topographical conditions at high altitudes are more irregular, the irreg- 
ularity of rainfall distribution due to altitude is more pronounced. 

The mean annual rainfall map of New England (see Fig. 160, 
page 288) illustrates the influences of altitude, topography and geo- 
graphical location. From the coast the rainfall gradually increases as 
the White Mountains are approached and reaches a maximum of 
85.53 inches at the station on the top of Mount Washington. To the 
west of the White Mountains, there is a material decrease in rainfall 
probably due to distance from the ocean and the low intervening ele- 
vation. The rainfall is increased somewhat by the altitude of the 
Green Mountains of Vermont, but no data are available as to the maxi- 
mum precipitation on their summits. That such an increase is pos- 
sible is evident, but it is not sufficiently assured to warrant any con- 
siderable investment based on such an increase. 

In the State of Maine the precipitation seems to decrease almost di- 
rectly with the distance from the ocean, but westward from the coast 
of Massachusetts and Rhode Island there is an increase in rainfall as 
the distance from the ocean increases that cannot be attributed, except 
in a minor degree, to the effect of altitude. 

To the southwest, the altitude of the Catskill Mountains undoubt- 
edly induces increased precipitation (see Fig. 161, page 291) and yet 
the irregularity of the relations of altitude and intensity on the differ- 
ent portions of the mountains seems to be greater than would normally 
be accounted for by distance from the sea, and illustrates the inade- 
quacy of our knowledge as a basis for estimating such relations with- 
out extensive precipitation data. 



Southern California. 



29 



139. Southern California. — The effect of altitude on rainfall inten- 
sity often becomes more obvious in arid countries and is frequently of 
much greater importance in local engineering problems. Southern 
California while bordered by the Pacific Ocean is far from the normal 




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Fig. 161. — Average Annual Rainfall in the Region of the Catskill Mountains 

(see page 290). 



292 



Rainfall and Altitude. 



paths of storm centers. The normal annual rainfall of the level coun- 
try is therefore low and the importance of conserving the flow of 
streams for water supply and irrigation is very great. San Diego lo- 
cated close to the ocean has an average annual rainfall of 9.62 inches, 
while at Salton, about 80 miles from the coast, behind the Coast Range 
and about 260 feet below sea level, the average annual rainfall is about 
three inches. In the mountains to the eastward and near the Coast, 
the rainfall is greatly increased and such increase must be considered 

6000 



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Fig. 162. — Altitude-Rainfall Diagram for San Diego and Vicinity. 

in various engineering problems. 1 Considerable rainfall data are avail- 
able in this region and approximate isoheytal lines may be constructed 
which will serve more or less as a g"uide in such estimates. It is 
found, however (see Fig. 162), that altitude alone is not a safe guide 
to amount of rainfall for while as a general rule for this region 
average annual amount increases with altitude, this increase may be 
from .4 inch or less per 100 feet to .8 inch or more per 100 feet of rise. 
These ratios represent differences in local precipitation much greater 
than would at first appear for it should be noted that at Warner's 
Springs (elevation 3,165) there is an average annual rainfall of 
16 inches, while at Mesa Grand (elevation 3,300) there is an average 
annual rainfall of 30.70 inches. Note also the increase in rainfall from 
Escondido (el. 657) to Warner Springs (el. 3165) is only 0.93 inches, 



1 Construction of the Morena Dam, San Diego County, California, by M. M. 
O'Shaughnessy. Trans. Am. Soc. C. E., "Vol. 75, page 27. 



Southern California. 



!93 



while the comparison of the rainfall of Valley Center (el. 1365) with 
Warner Springs shows a decrease in average annual rainfall of nearly 
4 inches with a rise of 1800 feet. 




Fig. 163. — Topographic Map of San Diego and Vicinity Showing Relative 
Locations of Rainfall Stations. 

In making estimates of the rainfall at intermediate stations within 
this area, great care is therefore needed to secure results which are 
even approximately correct. 

The mean annual rainfall (1910) at various stations in San Diego 
County and vicinity is given in Table 31, together with the elevation 



294 



Rainfall and Altitude. 



of the station. 2 A topographical map, based on the maps of the U. S. 
Geological Survey, showing the relative locations of rainfall stations is 
shown in Fig. 163. 

On this map all areas lying above elevation 2,000 feet are cross 
hatched. 

TABLE 31. 

Rainfall Stations, San Diego County, California, and Vicinity. 

Length of Elevation Average 

observation above sea level annual rainfall 

Period, years Feet Inches 

Nellie 7 5,300 44.26 

Cuyamaca Reservoir 21 4,677 38.84 

Julian 28 4,250 26.36 

Noble's Mine 3 4,200 24.5 

Buckman Springs 2 3,500 19.90 

Mesa Grande 5 3,300 30.70 

Morena Dam 5 3,300 24.15 

Warner's Springs 4 3,165 16.08 

Santa Ysabel 10 2,983 24.17 

Campo 31 2,189 19.98 

Barrett Dam 5 1,600 19.07 

Valley Center 26 1,365 20.03 

Elsinore 12 1,234 13.64 

Jamul 6 900 13.00 

Fallbrook 27 700 17.14 

Escondido 14 657 15.15 

El Cajon 10 482 12.24 

Foway 29 460 13.79 

Sweetwater Dam 20 238 9.52 

San Diego 53 87 9.62 

Salton Sea 30 —260 3. 



TABLE 32. 

Rainfall Stations in Southern Arizona and New Mexico. 

Length of 
Station observation 

period, years 

Luna, N. M 14 

Rosedale, N. M 11 

Flagstaff, Ariz 22 

Bluewater, N. M 14 

Ft. Bayard, N. M 46 

Pinto, Ariz 10 

Snowflake, Ariz 12 

Lake Valley, N. M 10 

Ft. Buchanan, Ariz 4 

Bisbee, Ariz 25 

Prescott, Ariz 48 

Ft. Apache, Ariz 41 

Ft. Huachuca, Ariz 30 

Holbrook, Ariz 24 

2 Tbid, page 54. 



Altitude 


Average 


above sea 


annual rainfall 


level, feet 


inches 


7,300 


15.94 


6,900 


19.26 


6,907 


22.96 


6,732 


9.53 


6,152 


15.42 


5,660 


11.49 


5,644 


10.27 


5,413 


14.71 


5,330 


21.58 


5,350 


18.44 


5,320 


17.21 


5.200 


17.87 


5,100 


17.06 


5,069 


9.30 



Rainfall Stations, Arizona and New Mexico. 295 



TABLE 32— Continued. 
Rainfall Stations in Southern Arizona and New Mexico. 

Length of Altitude Average 
Station observations above sea annual rainfall, 

period, years level, feet inches 

Ft. Grant (Bonita) Ariz 39 4,916 14.27 

Alma, N. M 18 4,800 15.65 

Jerome, Ariz 17 4,743 18.92 

Tombstone, Ariz 17 4,550 13.85 

Pinal, Ariz 23 4,520 23.45 

Oracle, Ariz 19 4,502 19.50 

Gage, N. M 16 4,420 10 21 

Mimbres, N. M 4,339 18-42 

Deming, N. M 39 4,333 10.03 

Tonto, Ariz 13 4,300 15.15 

Cochise, Ariz 25 4,250 11.69 

Lordsburg, N. M 26 4,245 9.36 

Wilcox, Ariz 35 4,203 10.91 

Gila, N. M 8 4,040 14.50 

Douglas, Ariz 20 3,930 15.03 

Nogales, Ariz 17 3,830 13.97 

Breckinridge, Ariz 6 3,800 17.03 

Bowie, Ariz 35 3,756 14.10 

Globe, Ariz 15 3,625 16.71 

San Simon 25 3,609 7.86 

Clifton, Ariz 25 3,584 13.55 

Benson, Ariz 34 3,523 9.47 

Kingman, Ariz 13 3,326 11.02 

Vail, Ariz 26 3,241 10.69 

Verde, Ariz 22 3,160 13.13 

Ft. Thomas, Ariz 26 2,816 11.46 

Thatcher, Ariz 17 2,800 10.23 

Rice, Ariz 33 2,540 11.30 

San Carlos, Ariz 25 2,456 12.91 

Tucson, Ariz 49 2,400 11.74 

Cline, Ariz. . . : 14 2,300 15.49 

Dudleyville, Ariz 23 2,204 14.59 

Wickenberg, Ariz 14 2,072 9.47 

Redrock, Ariz 12 1,864 11.18 

Florence, Ariz 18 1,493 9.88 

Casa Grande, Ariz 26 1,396 5.76 

McDowell, Ariz 23 1,250 10.38 

Mesa, Ariz '. . 19 1,244 8.78 

Maricopa, Ariz. 36 1,180 6.19 

Phoenix, Ariz 24 1,100 8.00 

Buckeye, Ariz 24 980 7.34 

Sentinel, Ariz 16 685 4.00 

Gila Bend, Ariz 25 787 5.82 

Mohawk, Ariz 28 538 3.32 

Aztec, Ariz 9 492 3.92 

Parker, Ariz 19 353 4.82 

Yuma, Ariz 35 140 3.00 

140. Southern Arizona. — The relation of altitude to mean annual 
rainfall intensity in Southern Arizona is shown by Fig. 164, page 296. 

The solid inclined lines on this figure indicate rates of increase of 



296 



Rainfall and Altitude, 



rainfall with altitude, while the dashed lines show rules or formulas 
suggested for this region. The approximate topographical conditions 
surrounding the various stations are shown in Fig. 165, page 297, in 



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Fig. 164. — Altitude-Rainfall Diagram for Southern Arizona (see page 295). 

which the areas lying above elevations of 5,000 feet are shown cross 
batched. In Arizona as in Southern California the general increase 
of intensity with altitude is at once apparent from Fig. 164; but a 
brief examination of the data will indicate the great danger of error in 
any estimate of the average intensity of the annual rainfall for inter- 



Southern Arizona. 



297 



~ r '"y T ^"W~^T 





298 



Rainfall and Altitude. 



mediate stations. The great range in the average amount of annual 
rainfall at various stations beween 4,000 and 5,000 feet in altitude 
should be noted. Table 32 gives the rainfall stations in the area to- 
gether with the period of observation, altitude above sea level and 
mean annual rainfall of each station. Several attempts have been 

8000 



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5 



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Average tfnnuo/ £?ainfo// in Inches 

Fig. 166. — Altitude-Rainfall Diagram for Southern Utah. 

made to establish definite rules for calculating these relations for parts 
of this territory, which are discussed in Section 143. 

141. North Eastern Utah. — The distinct increase of average annual 
rainfall with altitude is not always as definite as in the cases discussed 
in Sections 139 and 140. In northeastern Utah west of the Wasatch 
Mountains, the Great Salt Lake seems to have an influence on the 
rainfall of the stations to the east which almost entirely obscures the 
effect of altitude. Here a few miles distance from the lake seems to 
have a much greater effect than a considerable difference in altitude. 
These relations are shown in Fig. 166, and the approximate topographi- 
cal conditions are shown in Fig. 167 in which the cross hatched por- 



Northeastern Utah. 



299 




Fig. 167. — Topographic Map of Northeastern Utah. 



300 



Rainfall and Altitude. 



tion indicate elevations above 7,000 feet. The effects of Great Salt 
Lake are further emphasized by the low precipitation at stations south 
of the lake and away from the ordinary paths of atmospheric move- 
ment over this body of water. The influences of locations beyond the 
divide are also obvious. It should also be noted that a line passing 



TABLE 33. 

Rainfall Stations in Utah. 

Length of Elevation Average 

observations above sea annual rainfall, 
Station period, years level, feet inches 

Soldiers Summit 12 7,425 12.10 

Oakley 4 6,750 21.2 

Woodruff 4 6,500 10.01 

Meadowville 14 6,200 17.41 

Heber 22 5,620 17.46 

Manti 20 5,575 12.10 

Theodore 3 5,507 9.92 

Castledale 16 5,500 8.63 

Henefer 15 5,301 19.30 

Sunnyside 5 5,282 14.86 

Govt. Creek 14 5,277 13.44 

Scipio 20 5,260 15.22 

Thistle 21 5,075 14.76 

Levan 19 5,010 16.38 

Promontory 30 4,913 8.23 

Alpine 8 4,900 19.28 

Tooele 19 4,900 15.93 

Elberta 13 4,650 10.06 

Mt. Nebo 8 4,650 10.53 

Deseret 20 4,541 7.88 

Provo 21 4,532 14.20 

Logan 24 4,507 15.97 

Salt Lake 41 4,366 16.03 

Ogden 44 4,310 14.55 

Parmington 10 4,267 21.17 

Corrinne 45 4,240 12.51 

Saltair 11 4,220 15.15 

near Saltair, Heber and Oakley, seems to indicate a certain approxi- 
mate relation of altitude to rainfall intensity in one direction, conclu- 
sions from which would be quite different from those which would be 
drawn from a similar line drawn near Saltair, Provo, Thistle and Sol- 
dier's Summit. It should also be noted that the difference in rainfall 
between Salt Lake City and Alpine or Farmington cannot reason- 
ably be attributed to distance from the lake or difference in altitude 
but must be due to the local direction of moist air currents not to be 
accounted for without much fuller information than is here available. 
Table 33 gives the rainfall stations in this area together with the period 



Relations During Single Storms. 



30 



of observation, altitude above sea level, and the mean annual rainfall 
of each station. 

142. The Relations of Altitude and Rainfall During Single 
Storms. — The relation of average annual rainfall to altitude is modi- 
fied by the many fortuitous circumstances which surround the occur- 
rence of the numerous local and general rainstorms of which these an- 
nual means are made up. A study of single storms may give a more 



5000 



3000 



S EOOO 



/ooo 




eo /so /so eoo 2^0 

D/sfa-rrce fKorrt Secrcoasf, A7//es. 



300 



Fig. 168. — Topographic and Rainfall Profiles for the Storm of July 14-17, 
1916, in the Carolinas (see page 302). 

distinct idea of the influences of various factors on the main problem. 
The great storm which occurred in the South Atlantic and East 
Gulf States, July 14 to 17, 1916, has been briefly discussed (see 
Section 85) and illustrated (see Figs. 95 and 96, pages 174 and 
175). As is ordinarily the case with rainstorms which accompany 
West Indian hurricanes, a considerable rainfall occurred close to the 
point at which the hurricane path first encountered the land. In most 
cases the rainfall of the interior rapidly decreases as the distance from 
the Coast increases. In this case, however, the hurricane moved di- 
rectly toward the southeastern spur of the Alleghenies and was ap- 
parently dissipated thereby. The altitudes encountered induced a 
still heavier rainfall on the mountain slope and a record precipitation 



302 



Rainfall and Altitude. 



on or near the summit. Fig. 168 shows the profile of the land surface 
on a line from near Georgetown, S. C. to Altapass, N. C. On this 
profile is also shown the location and comparative elevation of various 
stations on or adjoining the line of this profile, and above each is 
platted the depth of rainfall that occurred during his storm. This 




Pig. 169. — Topographic and Rainfall Map of the Los Angeles District (see 

page 303). 

profile shows the great rainfall which occurred closely adjacent to the 
Coast and the greater rainfall on the mountains. A heavy rainfall 
was apparently also induced in the region just beyond the divide, and 
the radical decrease in precipitation at Elizabethtown about 30 miles 
farther on is also shown. 

An unusually heavy rainstorm occurred in the Los Angeles district 
in Southern California, Feb. 18 to 21, 1914. This rainfall was oc- 
casioned by a storm the center of which slowly approached the north- 
ern Pacific Coast, passed over Port Crescent Feb. 22, and was appar- 



Relations During Single Storms. 



303 



-ently dissipated in the mountains. Its slow movement gave rise to 
far reaching effects, as is shown by the unusual precipitation in South- 
ern California. Fig. 169 is a topographical map of the Los Angeles 
region on which have been drawn isohyetals 3 which indicate in a gen- 
eral way the effect of elevation on the rainfall intensity. Distance 
from the sea here seems to have little effect, the apparent factors being 



6000 
























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5000 




























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! 






















i 






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4000 






















<0 










1 


















N 


t 










\ 


3000 


























1 


v 












^ 
< 

X 


















\J 


2000 












^^ 




















1 


ffa/'r? 


eg// ^ 


proj 


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f Groc/r?a' f 3 /- 


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4 8 /£ 16 20 24 28 32 

D/stortce frorr? Seercoosr, A7//&S 

Fig. 170. — Topographic and Rainfall Profiles for the Los Angeles District. 

the direction of the air currents and altitude. Fig. 170 shows a profile 
of surface elevations and of rainfall intensities based on the records of 
stations closely adjoining a line drawn from San Pedro to Mount Wil- 
son. Table 34 gives the rainfall stations in this area together with the 
period of observation and altitude above sea level at each station. 

It is pertinent and instructive to add that the relations of altitude to 
intensity of precipitation as indicated by the records at Los Angeles 
and Mount Lowe are not alone indicated by individual rain storms but 
are also clearly shown by the average monthly and annual precipita- 
tion at these two stations as shown graphically by Fig. 171. 4 It is to 
be noted, however, that the rainfall for each individual storm or for 



3 Flood Studies at Los Angeles, F. A. Carpenter. Monthly Weather Review, 
.1914, page 385. 

4 Ibid, page 385. 



304 



Rainfall and Altitude. 



TABLE 34. 
Rainfall at Stations Near Los Angeles Cal, 



Station 



Elevation, 


Jan. 12-19, 


Jan. 22-29, 


Feb. 18-21. 


feet 


1916 


1916 


1914 




inches 


inches 


inches 


30 






3.45 


540 


12.30 


4.56 


13.26 


4,600 






10.83 


714 






4.81 


1,200 


10.80 


4.74 


10.92 


4,537 






17.85 


615 


8.28 


6.16 


4.31 
8.63 


1,334 






4.85 


470 






6.44 


536 






9.41 


1,316 






5.68 


400 






6.75 


47 






3.24 


293 


6.90 


3.49 


7.07 


2,950 


7.36 


6.16 


11.10 


3,500 


11.40 


3.76 


19.20 


5,850 


13.40 


5.90 


19.40 


176 






3.55 


584 






3.90 


1,100 






3.87 


827 


8.82 


3.49 


11.44 


857 


10.50 


4.92 


9.60 


1,352 


5.84 


3.33 


4.26 


16 






3.51 


851 


4.80 


3.53 


2.79 


1,888 






12.25 


1,066 


8.47 


3.55 


8.88 


1,054 


8.75 


4.57 


4.71 


909 






11.29 


19 


3.00 


2.60 


2.03 


110 


7.14 


4.13 


5.50 


1,400 


10.21 


4.27 


15.56 


5,280 


27.78 • 


10.86 


16.29 


125 


4.01 


3.83 


3.52 


3,750 


5.16 


0.58 


5.57 


25 






5.16 


50 






10.21 


600 






6.96 


246 






5.02 



Avalon 

Azusa 

Bear Valley Dam.. 

Chino 

Claremont 

Cleghorn Canyon . . 

Corona 

Devil Canyon 

East Highlands . . . 

Fillmore 

Garvanza* 

Highland 

Hollywood* 

Long Beach 

Los Angeles 

Mill Creek 

Mt. Lowe 

Mt. Wilson 

Orange 

Palm Springs 

Palos Verde 

Pasadena 

Pomona 

Redlands 

Redondo 

Riverside 

San Antonio Canyon 

Pacoima 

San Bernardino . . . 

San Dimas 

San Pedro 

Santa Monica 

Sierra Madre 

Squirrel Inn 

Tustin 

Valyermo 

Venice 

Ventura 

Walnut 

Whittier 

* Suburb of Los Angeles. 

each individual month or year does not uniformly show such relations. 
(See Table 35.) 

143. Rules for Estimating Relations of Altitude to Rainfall.— 
While it has been possible to discuss in this chapter the relation of alti- 
tude to rainfall in only a few local districts, enough has been said and 
shown to emphasize the fact that any rule for estimating such relations 



Estimating Relations. 



305 



TABLE 35 

Comparison of rainfall of Los Angeles and Alt. Lowe 





Jan. 


Feb. 


Mar. 


Apr. 


May 


June 


July 


Aug. 


Sept. 


Oct. 


Nov. 


Dec 




1896 


Los Angeles 
Mt. Lowe... 


3.i3 

2.85 


T 

0.10 


2.97 
4.10 


0.19 
0.60 


0.30 
0.30 


T 

0.00 


0.02 
0.00 


0.01 
0.10 


T 

0.00 


1.30 
2.39 


1.66 
1.55 


2 12 
2.17 


11.80 
14.16 


1897 


Los Angeles 
Mt. Lowe . . 


3.70 
6.42 


5.62 

7.47 


2.31 
6.67 


0.02 
0.19 


0.10 
0.87 


T 

0.10 


T 

0.15 


0.00 
0.00 


0.00 
0.00 


2.47 
2.57 


0.01 
0.40 


0.05 
0.22 


14.28 
25.06 


1898 


Los Angeles 
Mt. Lowe .. 


1.26 
1.55 


0.51 
2.22 


0.98 
1.65 


0.03 
2.70 


1.75 
2.17 


T 

0.00 


07 
0.00 


T 

0.00 


0.02 
0.25 


0.09 
0.30 


T 
0.90 


0.12 
0.98 


4.83 
11.82 


1899 


Los Angeles 
Mt. Lowe .. 


2.64 
3.29 


0.04 
0.00 


1.81 
3.40 


0.18 
0.20 


0.04 
1.90 


0.58 
0.40 


0.00 
0.00 


0.01 
0.00 


T 

0.00 


1.59 
3.00 


0.90 
2.85 


0.90 
2.14 


8.69 
17.18 


1900 


Los Angeles 
Mt. Lowe . . 


1.17 

5.50 


T 

5.03 


0.99 
2.90 


0.54 

2.15 


1.81 
4.05 


T 

0.40 


T 
T 


T 
0.00 


T 
0.25 


0.26 

1.66 


6.53 
11.71 


T 
0.00 


11.30 
33.65 


1901 


Los Angeles 
Mt. Lowe . . 


2.49 
7.55 


4.38 
5.42 


0.45 
1.18 


0.68 
1.14 


1.50 
4.45 


T 

0.75 


T 

0.00 


9.69 
0.00 


03 
0.00 


1.88 
4.18 


0.46 
1.05 


0.00 
0.23 


11.96 
25.95 


1902 


Los Angeles 
Mt. Lowe . . 


1.62 
1.88 


3.35 
3.48 


3.98 
5.97 


0.16 
1.35 


0.03 
0.33 


T 

0.30 


T 

0.00 


T 

0.00 


T 

0.00 


0.40 
0.90 


2.08 
3.68 


2.50 
2.14 


13.12 
20.03 


1903 


Los Angeles 
Mt. Lowe 


2.10 


1.52 


6.93 


3.77 


T 


0.02 


0.00 


T 


0.43 


T 


0.00 


T 


14.77 


1904 


Los Angeles 
Mt. Lowe . . 


0.14 
0.00 


2.68 
4.02 


4.50 
6.92 


0.97 
2.10 


T 

0.20 


T 
0,00 


T 

0.00 


0.17 

1.27 


0.28 
1.50 


0.69 
0.00 


0.00 
0.00 


2.45 
1.98 


11.88 
17.99 


1905 


Los Angeles 
Mt. Lowe .. 


2.57 
4.02 


6.06 
12.53 


6.00 
10.56 


0.35 
1.07 


0.95 
4.01 


0.00 
0.00 


0.00 
0.00 


0.00 
0.00 


T 
0.00 


0.08 
0.24 


2.98 
3.74 


0.20 
0.12 


19.19 
36.29 


1906 


Los Angeles 
Mt. Lowe . . 


3.85 

4.55 


2.47 
3.80 


7.35 
18.66 


0.69 
2.28 


1.02 
3.50 


0.01 
0.00 


0.02 
0.00 


0.03 
0.22 


0.05 
0.00 


0.00 
0.00 


0.85 
1.04 


5.12 
11.85 


21.46 
41.90 


1907 


Los Angeles 
Mt. Lowe .. 


7.02 

12.83 


1.83 
3.60 


4.12 
7.24 


0.16 
1.90 


0.07 
0.89 


0.03 
0.94 


0.00 
0.00 


0.00 
0.00 


T 

0.00 


1.18 
3.36 


T 

0.05 


0.88 
1.67 


15.30 
32.48 


1908 


Los Angeles 
Mt. Lowe .. 


5.04 
6.84 


3.66 
5.56 


0.18 
1.02 


0.52 
1.90 


0.25 
0.95 


0.00 
0.00 


T 

0.00 


0.08 
0.00 


1.22 

2.48 


0.25 
0.80 


1.08 
0.75 


1.46 
2.13 


13.74 
22.43 


1909 


Los Angeles 
Mt. Lowe .. 


7.27 
14.22 


5.20 
11.94 


2.51 

7.38 


T 
0.56 


0.00 
0.03 


0.11 
0.75 


0.00 
T 


T 
1 0.02 


0.04 
0.15 


0.28 
1.40 


1.51 
3.10 


7.00 
18.98 


23.92 
251.53 


1910 


Los Angeles 
Mt . Lowe . . 


1.53 
1.40 


0.11 
O.U 


1.86 
3.80 


0.30 
0.27 


0.00 
0.02 


0.00 
0.00 


0.04 
T 


T 

0.0 


0.01 
0.00 


0.82 
1.05 


0.15 
1.57 


0.07 
l 0.07 


4.89 
3 8.32 


1911 


Los Angeles 
Mt. Lowe . . 


6.70 
15.76 


2.91 
4.37 


5.15 
5.95 


0.28 
1.90 


0.02 
0.25 


0.03 
0.00 


T 

0.00 


O.fO 
0.00 


1.23 
2.00 


0.16 
0.20 


0.1U 
0.22 


1.27 
1.25 


17.85 
31.90 


1912 


Los Angeles 
Mt. Lowe . . 


07 
0.5U 


0.00 
O.iO 


6.99 
8.12 


1.66 
2.67 


0.12 
0.87 


0.00 
0.(0 


T 

0.00 


0.00 
0.00 


0.0' 

0.00 


0.56 
2.20 


0.35 
0.60 


0.03 
T 


9.78 
14.96 


1913 


Los Angeles 
Mt. Lowe . . 


2.01 
3.16 


9.16 
11.60 


0.33 
0.76 


0.35 
0.98 


0.05 
T 


0.58 
1.65 


T 

0.05 


T 

0.03 


0.03 
0.05 


T 
T 


3.00 
4.00 


1.66 
2.85 


17.17 
25.10 


1914 


Los Angeles 
Mt. Lowe .. 


10.35 
12.70 


7.04 
19. 2J 


0.58 
1.30 


0.47 
2.12 


0.43 
0.98 


0.09 
0.20 


0.01 
T 


0.00 
0.0 J 


0.00 
0.00 


0.31 
1.43 


0.20 
T 


3.73 
5.80 


23.21 
43.73 


1915 


Los Angeles 
Mt. Lowe . . 


5.42 
8.60 


5.09 
8. 00 


0.60 
1.22 


0.81 
2.44 


0.88 
2.45 


T 

o.co 


0.00 
0.00 


0.00 
0.00 


T 

0.10 


0.00 
0.00 


1.35 
2.00 


2.52 
2.70 


16.67 
27.51 


1916 


Los Angeles 
Mt. Lowe 


13.30 

19.86 


1.82 
2.87 


0.90 
4.15 


T 

0.00 


0.03 
0.00 


0.00 
0.00 


0.00 
0.00 


T 

0.00 


0.77 
1.80 


2.71 
5.00 


0.09 
0.30 


3.67 

6.40 


23.29 
40.38 



i Estimated 

2 Includes estimated 

a Includes estimated 



total for August 
total for Decern ber 



Hydrology — 20 



306 



Rainfall and Altitude. 



must be purely local. Even in these cases rules must be regarded 
as subject to possible exceptions which may greatly affect the accuracy 
of estimates based thereon. The very statement of the attempted 
rule often shows the difficulties in its application. 

On the north slope of the French Alps, at the elevation of 1,5(30 me- 



Mar. 




Apr. 



May 






/"> 




r\ 
















1 


n 




\ 


























WW 


Low 
















/ 


" 


\ 




















Los Anoe/esfr- — 














_,_ 


--' 


1 I \s- 





O. 






^ 


•'' 







Jan Feb Mor Apr.Moy Jun Jut Aoa. Sept Oct A/ov. Dec 



Fig. 171. — Average Rainfall at Los Angeles and Mt. Lowe (see page 303). 

ters, an average rainfall of 1,500mm has been observed; and it is as- 
sumed that as a general average, the rainfall in the regions above 
1,500 meters increases by 150 to 250 mm for every 100 meters eleva- 
tion. Certain small regions may, of course, have results that differ 
from this arbitrary rule. 5 

In Austria the plains have the least rainfall. In Central Bohemia 
and in Mahren and Lower Austria, etc., the yearly rainfall decreases 
to 200 to 300 mm. The following table, compiled by Bebber, shows 
the effect of elevation upon rainfall : 6 

From 



100- 200 


m. 


above 


sea 


level 


583 mm 


200- 300 










650 


300- 400 










696 


400- 500 










782 


500- 700 










852 


700-1,000 










995 


1,000-1,200 










1,308 



5 Der Wasserbau, 1907, Th. Koehn. 

« Frederick Kulturtechnischen Wasserbau. 



Estimating Relations. 307 

Usually attempts to formulate the relation of rainfall to altitude 

haA^e been expressed by a straight line equation : 7 

A 

R' = R + K 

100 

in which R' and R are average annual rainfalls at the higher and lower 
points respectively, A is the difference in altitude in feet, and K is a 
constant for the region. Values of K range from two-tenths to eight- 
tenths of an inch in the West, six-tenths being frequently used for the 
Sierras of California. A value of 0.21 was derived by Mr. J. B. Lip- 
pincott for the Gila and Salt River Basins in Arizona. 8 The rule 
which was formulated by Lippincott about 1899 still seems in the light 
of seventeen years additional data to apply with reasonable accuracy 
to the local conditions in this valley. It should be used, however, only 
after careful consideration of the local condition of the area for which 
an estimate is to be made. 

Prof. G. E. P. Smith has sought to establish such relations for certain 
areas in Southern Arizona. 8 He has suggested two curves, one for 
Cochise and Graham Counties, and the other for Pima and Pinal Coun- 
ties. The author has been unable to ascertain any adequate reason for 
the differentiation between these Counties, or for the belief that there is 
any increase in annual rainfall above the 4000 foot contour. 

144. General Conclusions. — While in general rainfall will increase 
with altitude, it is dangerous to assume that this will always be the case, 
as there are many exceptions to this rule. Where the rule holds, the 
amount of such increase is difficult and often impossible to determine. 

An assumption of large runoff for mountain streams based solely 
upon elevation where no records of mountain rainfall or runoff are 
available, is unsafe and does not warrant large investments in projects 
based upon such assumptions. 

LITERATURE. 

The Relation of Rainfall to Mountains, W. H. Alexander. Monthly Weather 

Review, 1901, p. 6. 
Relation of Rainfall to Runoff in California, J. B. Lippincott and S. G. Bennett. 

Eng. News, Vol. 47, 1902, p. 467. 



" Rainfall and Surface Waters, G. E. P. Smith. Bui. 64, Arizona Agricul- 
s Bulletin 64, Arizona Agricultural Experiment Station. 

tural Experiment Station. 

s Ground Water Supply and Irrigation in Rillito Valley, G. E. P. Smith. 

Univ. Arizona Agric. Exp. Sta., Bui. 64, 1910. 



308 Rainfall and Altitude. 

The ^TJieory of the Formation of Precipitation on Mountain Slopes. Prof. E. 

Pockels. Monthly Weather Review, 1901, p. 152 
See also "Mechanics of the Earth's Atmosphere," Smithsonian Miscella- 
neous Collection, Vol. 51, No. 4, Article VIII. 
Effects of Mountains on Humidity, Cloudiness and Precipitation, Dr. Julius 

Hann. Handbook of Climatology, translated by R. De C. Ward. The 

MacMillan Co., 1903. 
Rainfall in England in Relation to Altitude, W. Marriott. Quar. Jour. Royal 

Met. Soc, Vol. 26, 1900, p. 273. 
Precipitation and Altitude in the Sierras, Chas. H. Lee. Mon. Weath. Rev., 

July, 1911, p. 1092. 
Ground Water Supply and Irrigation in Rillito Valley, G. E. P. Smith. Univ. 

Ariz. Agric. Exp. Sta., Bui. 64, 1910. 



CHAPTER XIII 
GEOLOGICAL AGENCIES AND THEIR WORK 

145. Hydrological Influence of Topography and Geology. — The 

geology of a district and its accompanying topographical and strati- 
graphical conditions greatly modify its hydrological phenomena. Sharp 
topographical relief, as shown in Chapter XII, exerts a notable influ- 
ence, quantitatively uncertain, by increasing precipitation on the wind- 
ward side and decreasing precipitation on the leeward side of consider- 
able elevations. The character of the material and the dip of the strata 
have had a marked influence on the trend of the development of streams, 
and still have such influence on the effect of the flow on the denudation 
of the exposed strata. 

The structure, extent of outcrop and slope of the strata have an im- 
portant effect on the disposal of rain waters and greatly modify the rela- 
tive amounts of evaporation, absorption and surface flow. These same 
factors, together with the amount and distribution of the precipitation 
received on the exposed outcrops of the strata, are the controlling ele- 
ments which modify the presence and flow of underground waters. 
The surface slope of the country and the character of the rocks com- 
posing the drainage area, together with the amount and distribution of 
the precipitation, are controlling factors in the character of runoff or 
stream flow. All of these factors are in turn modified by geographical 
and climatic conditions. A study of local geological history gives in- 
dications of the possible or probable character and extent of the under- 
lying strata and is prerequisite to intelligent local investigations. 

The present conditions have been brought about through agencies 
that are still active and which are still impressing their influence on the 
earth's surface. While the activity of these agencies may have been 
modified by changes in climatic and other conditions, the general nature 
of their action remains unchanged and a study of their past effect will 
give an intelligent basis for the type of construction necessary to utilize 
these agencies for the benefit of mankind. 

For a proper knowledge of the hydrological conditions of any district, 
an understanding of historical and general geology and of the character 
of the agencies and sequence of events that led up to the local geological 
conditions that now obtain, is frequently indispensable. 



310 Geological Agencies. 

In a general treatise on hydrology it is possible to discuss geology in a 
very general way only, and to consider in greater detail but still in a 
most general way, a few of the most important factors and conditions 
which influence or control the problems of the hydraulic engineer. The 
knowledge of general geology necessary for a clear conception of many 
problems in engineering, as well as the detailed study of the more or 
less local conditions which for successful results must be investigated 
and understood, can be secured by the engineer from the many special 
treatises on these subjects. 

146. Outline of Causes Productive of Topographical and Geo- 
logical Changes. — The following is a summary of the agencies that 
have been active causes of the evolution of the earth's surface from 
past to present structure and form. These agencies are still active and 
operative, and an appreciation and knowledge of them are essential in 
order that the engineer may design his structures for stability and per- 
manency so far as possible. 

A. Factors of Disintegration: 

(a) Rock Texture: 

Resistant — Capable of withstanding erosive agencies for 

considerable periods. 
Yielding — Easily eroded. 

(b) Vegetation : 

Wedging action of plant roots. Decay of vegetation re- 
sults in the formation of acids which increase solvent 
power of water. 

Retards surface erosion of soil where thick enough to 
form a protective covering. 

B. Factors of Erosion, Corrosion and Transportation: 

(a) Crust Movements: 

Unequal settlements resulting in oceans and continents. 
Upheavals resulting in islands and mountain ranges. 
Subsidence. Deep sea inlets, bays, etc. 
Volcanic. Limited but marked upheavals and subsidence, 
and ejection of molten matter. 

(b) Precipitation and Moisture: 

Concentration of rainfall tends to increase corrasion and 
transportation powers by increasing volume and ve- 
locity of runoff. 

Plumidity of atmosphere tends to check sudden and con- 
siderable variations in temperature. 



Causes of Topographical and Geological Changes. 3 1 1 

Rivers : 

Powers of corrasion, transportation and deposition de- 
pend on velocity and volume of flow and the material 
forming the river bed and banks. 

Ice: 

Corrasion by glaciers and avalanches. 
Transportation by river ice. glaciers and avalanches. 

(c) Ocean and Lake Movements : 

The waves on the lakes and seas erode the shores against 
which they impinge. 

The lake and ocean currents transport the materials 
eroded by the waves or discharged by the rivers and 
build up extensions to the land and independent banks 
in the open water where conditions favorable to depo- 
sition occur. 

(d) Atmospheric Movements : 

Less important than precipitation except in regions of low 

rainfall. 
Direct effect great in modifying evaporation and precipi- 
tation. 
Shifting of sand dunes. 
In moist climates dries earth to dust and transports dust 

and sand. 
In arid regions there is less rock decay and less vegetation 
to anchor the products of decay, action of wind erosion 
in carving rocks (sand blast effect) is often great. 
Creates waves and currents. 
147. Rock Structure and Texture. — The diastrophic movements 
which have taken place since the indurated formations were first laid 
down have resulted in the development of joints and fissures in all rock 
masses at and near the surface which have given greater or less access 
to the agents of disintegration into exposed rock masses. Rocks of 
massive structure with few joints and fissures and with small exposures 
and gentle slopes, and which are protected by mantle coverings, disin- 
tegrate slowly. On the other hand, bare rocks with open joints and 
fissures or those composed of alternate beds of hard and soft material 
having steep slopes or existing as exposed clefts from which loosened 
material is rapidly removed, are quickly disintegrated. 

In the same manner the texture of the rock has a considerable influ- 
ence upon the rapidity of disintegration. If the rock is close grained, 



3 1 2 Geological Agencies. 

impervious, composed of insoluble material and of a physical quality 
capable of standing erosive action, disintegration is slow. Pervious 
rocks of loose grain, composed of soluble material which is easily eroded, 
rapidly yield to disintegration. 

148. Erosion. — In order to understand the causes of topographical 
and geological changes, the extension and reduction of continental 
areas, the work of waves, tides and currents, the formation, extension 
and extinction of lakes, the development of drainage systems, the work 
of rivers and streams, and the consequent changes in the topography 
of their drainage areas, it is necessary to have a clear understanding of 
the manner in which the elements combine their actions and the meth- 
ods b)' which they accomplish their work. 

There are three principal methods by which the elements of erosion 
are continually reducing the heights of land toward what is termed the 
base level, which is approximately sea level, namely : weathering, cor- 
rasion, and transportation. 

Weathering is that continual decomposition and disintegration of the 
rock formations by which they are broken into fragments and reduced 
to the finest particles. 

Corrasion embraces the methods by which the action of running 
water reduces the masses of rocks by abrasion and solution. 

Transportation is the term applied to the conveyance from their 
original positions of fragments and particles produced by weathering 
and corrasion. 

The rapidity with which the various processes of erosion are carried 
on depends principally upon the texture of the deposits and on climate, 
and varies particularly with the abundance of rainfall. 

149. Weathering. — The weathering of rocks may be the result of 
chemical or mechanical processes. Through the agency of chemical 
action, portions of the cementing materials which bind the rock into a 
homogeneous mass are dissolved, thus promoting the disintegration of 
the rock. This action is greatly increased by various impurities which 
are frequently contained in the water, especially those derived from or- 
ganic decay. The action of gases in volcanic regions may be classed 
as a chemical process of weathering. The rapidity with which rocks 
disintegrate under the chemical processes of weathering depends 
mainly upon the composition of the rock, the composition and quantity 
of the water and the temperature. Under the mechanical processes of 
weathering may be classed the impact of falling rain, the wedging ac- 
tion occasioned by water freezing within the interstices of the rock, the 



Weathering. 



313 



wedging action caused by the roots of plants entering the crevices of 
the rock, and the variations in temperature, particularly rapid changes 
in temperature. In regions where the soil covering is derived from 
the native underlying rocks, the soil is entirely due to the effects of 
weathering, and the amount of such soil represents the rate at which 
weathering outdistances the rate of soil removal by transportation. 
The processes of weathering are largely responsible for the width of 
stream valleys, for by these agencies the rock is broken up and loosened 




Tic. 172. — Talus at the Base of Mountains around Moraine Lake, British Co- 
lumbia. 

from the sides of the hills and canyons, whence it falls to the stream 
by which it is broken up and carried away. 

The deep soil, which is the result of weathering when soil removal 
has not hitherto been active, is shown by Fig. 9, page 39. Fig. 172, 
shows the talus at the base of. the mountains surrounding Moraine 
Lake in British Columbia. This lake is of glacial origin and the talus 
represents the effects of weathering since the time when the valley was 
occupied by the glacier. 

150. Corrasion. — Corrasion is due in large measure to the abrasive 
action of material carried in suspension in running waters, and the 
larger part of this suspended matter is composed of material broken 
up and loosened by the processes of weathering. When the water of 
a stream runs over a bed of rock, the destructive effect is dependent 
itpon the velocity of flow, the depth of flow, the load of detritus it car- 



314 



Geological Agencies. 



ries, and the character of the rock ; in other words, the amount of work 
accomplished depends upon the material worked, the tools used and 
the energy expended. The principal work is accomplished by the 
boulders which are rolled along the stream bed (see Fig. 173), 
and since the size of the boulder moved by a stream varies as 




*.*■' 




Fig. 173. — Tools of the Stream, Boulders in the Spokane River. 

the sixth power of the velocity, the velocity is the important factor 
in influencing the rate of cutting. That a stream normally swift may 
be so loaded with detritus that its velocity is materially diminished, 
may readily be seen when it is considered that it is the bottom velocity 
and not the average velocity which is effective in cutting, and each ad- 
dition to its load reduces the energy of the flowing water by the amount 
necessary to carry the weight along. The maximum rate of corrasion 
therefore occurs when there is that balance beween velocity and load 
carried that permits of the most effective abrasive action by the debris 
upon the stream bed. In those regions where the large part of the 
yearly precipitation occurs as snowfall, and the summer temperatures 
are not sufficient to melt all the snow which fell in the previous season,, 
the greater part of corrasion and transportation is accomplished by 
the movement of glaciers. 

151. Erosion By Wave Action. — The nature of waves and the tre- 
mendous force of their impact have already been discussed in Sec- 



Erosion by Wave Action. 



315 



tions 55 to 60 inclusive. When waves beat against a shore, especially 
when they are loaded with debris, they may cause considerable erosion,, 
depending on the nature of the material of the land, the beach struc- 









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v' / 



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Fig. 174. — Coast Erosion by Waves. 




Fig. 175. — The Illecellewaet Glacier, British Columbia. 

ture, and the depth of water adjacent to the shore. The normal effect 
of the waves is both to cut a terrace in the shore line and by means of 
the receding waters to build up a terrace in the adjacent deep waters. 
(See Fig. 174). While the material eroded from the shore may 
furnish effective tools to assist corrasive action of the waves, un- 
less it is largely removed, either by falling into deep water or by cur- 



316 



Geological Agencies. 



rents, from those sections where erosion is in progress, it soon forms a 
protective covering and prevents further effective wave action. 

152. Glacial Erosion. — In the high mountains and in the poleward 
regions beyond the snow line where the summer heat is insufficient to 
melt the winter snows, snow fields are formed which by the accumu- 
lated pressure due to their great depths convert their lower portions 
into ice and force streams of ice slowly down the valleys (see Fig. 
175), until the end of the glaciers reaches a region where the 
summer temperatures are sufficient to limit the glacial movement. (See 




Fig. 176. — End of the Great Glacier, British Columbia. 



Fig. 176). The effect of these slowly moving masses of ice may 
easily be imagined. They grind down the valley bottoms and 
sides and often shove before them or carry within their structure or 
on their surface the materials which they have eroded or which 
through other causes have become disintegrated or broken from the 
valley structures and become imbedded in or deposited on the glaciers. 
This material is slowly moved forward and is finally deposited at the 
end or side of the glacier where the ice within or upon which it is trans- 
ported is melted by the temperatures of the valleys which limit its ad- 
vance. 

When the end of the glacier remains in one position for a long period 
and its movement is continually depositing material at its terminus as 
the ice melts, it builds up deposits which vary from low ridges to con- 
siderable hills and are called terminal moraines. Such deposits fre- 



Glacial Erosion. 317 

quently dam the waters of a valley from which the glacier has with- 
drawn and create lakes as in the case of the moraine below Moraine 
Lake in the valley of the Ten Peaks in British Columbia. (Fig. 
177). When the glacier is retiring, due to increased temperature 
or decreased precipitation, no moraine marks its terminus unless 
it becomes stationary at certain points for considerable periods, but the 
material carried is distributed over the bed which it formerly occupied. 




Fig. 177. — Terminal Moraine at the Outlet of Moraine Lake British Columbia. 

(Fig. 176.) Often much of the finer material is carried away by the 
glacial waters which result from melting. In other cases the glacier 
reaches the ocean before melting and breaks off in icebergs which float 
away, carrying with them the materials contained in their mass. (See 
Fig. 178, page 318). While glacial action is of comparatively little 
importance at the present time in the United States, such work is still 
in progress in the mountains of. the northwest, and most of Greenland 
and much of the polar regions are covered with perpetual ice. Much 
of the United States and of the northern portion of Europe and Asia 
have been greatly modified by such action during periods when glacial 
conditions were much more extended than at present. 

153. Movements of the Earth's Crust. — There are in general four 
ways by which the surface materials of the earth change their positions : 
First — By displacement or diastrophism when the crust of the earth is 

upheaved or depressed. 



318 



Geological Agencies. 



Second — By avalanches or landslides where unstable masses of rock 

slide into adjacent depressions. 
Third — By volcanic action or vulcanism when the earth's crust is 

rent and molten material is ejected. 
Fourth — By transportation when the material of the crust is broken, 

crushed, disintegrated and moved by the winds and waters from one 

region to another. 




Fig. 178. — Formation of Icebergs (see page 317). 



Diastrophism — The crust of the earth in many places rises and sink? 
but this action takes place so slowly that in few cases can the changes, 
he perceived except by comparison during long intervals of time. 

If the crust of the earth were uniform in elevation, the entire sur- 
face would be covered by water to an approximate depth of two miles. 
It is this diastrophic movement of the crust which has produced an un- 
equal surface and has given rise to the continents and islands. These 
land masses have changed and still are slowly changing their forms and 
extent as the surfaces rise, sink or perhaps remain stationary for a 
period of time. 

The main continent forming movements appear to have occurred 
prior to the formation of the earliest known sedimentary rocks. 1 
There have been times in past geological ages when great lateral 
thrust has occurred, perhaps through the cooling and shrinking of the 



1 See Chamberlain and Salisbury Geology, Vol. 1, p. 519. 



Movements of the Earth's Crust. 



319 



■earth's interior, and the surface strata have been warped and folded 
into mountain chains. This has usually occurred near the continental 
borders. The resulting folds are sometimes upright and symmetrical 
but more often inclined and unsymmetrical, and the strata are so 
warped, twisted and faulted as to make the age of the strata in a 
given vertical section not always in accord with their positions. In 
■other cases, great plateaus have been raised high above the oceans and 
more or less flexed, tilted and faulted but forming together vast high 
.and more or less level plains in which erosion lias had comparatively 
little effect in altering the main surface contours. These movements 
while still taking place are so slow that they have little effect in en- 
gineering works except that a knowledge of the conditions which have 
obtained in the past frequently furnishes a basis for understanding the 
•conditions which may be expected in carrying out such works. 





Fig. 179. — Dead Forest in Reelfoot Lake, Tennessee.3 

There have been times, as in the case of earthquakes, when crust 
movements have been immediately apparent and when fissures were 
formed in the crust, and one side has dropped and the other has been 
uplifted, either or both of which has occurred at the same period. In 
an earthquake that occurred in Japan in October, 1871, there was a 
vertical displacement of from two to twenty feet that could be traced 
for forty-six miles, and a horizontal displacement at one point of as 
much as thirteen feet. 2 Sometimes such movements interfere with the 
movements of ground water, new springs are formed and old ones 
cease to flow, and occasionally ponds and lakes are formed. 



- Chamberlain and Salisbury Geology, Vol. 1, p. 510. 



320 Geological Agencies 

In the earthquakes of 1811 and 1812 great depressions occurred 
near the Mississippi River in Kentucky, Tennessee, Missouri and Ar- 
kansas, and those areas became marshes and permanent lakes, in some 
of which standing trees are still visible. (See Fig. 179.) 3 

One of the most disastrous earthquakes of modern times occurred 
near San Francisco in 1906. This was caused by a new slipping on the 
old fault plane which has been traced for a distance of about 180 miles. 
(See Fig. 180.) The horizontal displacement shown by the existing. 




\j5ar? Juan 

Wonfereu 

Fig. 180. — Fault Line of the San Francisco Earthquake of 1906. 

roads, fences, etc. (see Fig. 181), was considerable. Many buildings 
and engineering works, pavements, pipe lines, etc., were destroyed by 
the shock, but the principal losses were caused by the resulting serious 
conflagration which destroyed most of the City of San Francisco. 4 

These disturbances are of great importance to the engineer who may 
have hydraulic works to construct in countries where earthquakes are 
liable to occur. Such structures must be carefully designed with such 
occurrences in view both for the safety of the structures and of the lives 
of the people which may depend upon such safety. 

Landslides — Masses of earth and rock on unstable slopes sometimes 
break away and slide into adjacent depressions. Conditions favorable 
to such occurrences exist where the masses overlie or consist largely of 
beds of soft incoherent material and especially where the bed joints are 
inclined toward the surface and the mass above has vertical jointing.. 



3 The New Madrid Earthquake, hy M. L. Fuller. 

4 The San Francisco Earthquake, by G. K. Gilbert, et al. 



Movements of the Earth's Crust. 



32 



The undercutting of streams and the saturation of the strata are factors 
which commonly make gravity effective in natural slides. 

In engineering works similar slides are caused by the weakening of 
strata by excavation for canals and railroad cuts or in mining and other 
works where masses of materials are removed from their natural beds. 
Such slides also occur in earth dams, reservoir embankments and levees 
where poor materials, improper construction or too great surface slopes 
are employed. 




Fig. 181. — horizontal Displacement During the San Francisco Earthquake 
shown by Road and Fence Line (see page 320 )A 

Vulcanism — Occasionally the crust has been rent by shocks, and 
molten matter is then sometimes ejected, pouring out in great streams 
of lava which spread over the surface and form extensive deposits. 
Such action at the present time has been extremely local in extent and 
outside of limited localities is of little importance to the engineer. 

Transportation — The runoff of the rainfall washes the sands and 
finer material from the mountains, hills and plains into the streams by 
which it is carried away and deposited on the lowlands, in the river 
channels or in the lakes and oceans where it is distributed by the cur- 
rents and waves and builds bars or forms new lands adjacent to the 
shores. 

Hydrology — 2 1 



322 



Geological Agencies. 



Transportation of material may occur in several ways. The fine 
fragmentary particles of the rock may be carried in suspension in the 
waters of the stream and the coarser portions may be rolled and pushed 
along the bed of the stream by the action of the current. Frequently 
the amount of the coarser materials that are moved along the bottom 
of the channel is very great. The amount of material so transported 
is dependent upon the velocity of the stream and its depth, together 
with the accessibility of material that can be carried. 




Fig. 182. — Deposits of Sand and Gravel behind the Danville Dam. 

Figure 182, shows the amount of material which had accum- 
ulated behind the dam at Danville, Illinois, in about a year after 
its construction. The dam built across the north fork of the Ver- 
million River was about thirteen feet in height and the stream which 
was of a somewhat flashy nature, during its rapid rises, not only car- 
ried a large amount of silt in suspension but also rolled along its bed 
large quantities of gravel and coarse sand which was stopped by the 
dam and accumulated until its top approached so near to the top of the 
dam that the velocity of the stream was sufficient to raise it over the 
crest. Hundreds of yards were deposited in this way, reducing the 
value of the storage pond which was formed by the dam. In this case 
the storage basin above the dam was not sufficient to prevent consid- 
erable current in time of flood and little or no silt was deposited except 
during very low floods. 



Movements of the Earth's Crust. 323 

Large boulders and other debris from the disintegration of the rock 
masses may fall or slide from the valley sides and find lodgment upon 
the river ice, or the ice may freeze to boulders along the bottom and 
shores of a stream, and upon breaking up in the spring, may trans- 
port them considerable distances. In the same way material is re- 

TABLE 36. 
Matter Carried in Solution and Suspension oy Various River Waters of the 

United States. 

Parts per million 
Stream Location In solution In suspension 

Arkansas Kittanning, Pa 82 100 

Allegheny Little Rock, Ark 

Big Vermillion Danville, 111 

Brazos Waco, Texas 1,136 

Cedar Cedar Rapids, Iowa 

Chippewa Eau Claire, Wis 

Colorado Austin, Texas 

Cumberland Nashville, Tenn 

Fox Ottawa, 111 

Hudson Hudson, New York 

Illinois LaSalle, 111 

Kentucky Frankfort, Ky 

Mississippi Dayton, Ohio 

Mississippi Minneapolis, Minn 

Mississippi Quincy, 111 

Missouri Memphis, Tenn 

North Platte Florence, Nebr 

Ocmulgee No. Platte, Nebr 

Potomac Macon, Ga 

Red Cumberland, Md 

iSt. Lawrence Shreveport, La 

Savannah Ogdensburg, N. Y 

Susquehanna Augusta, Ga 

Tennessee Danville, Pa 

Wabash Knoxville, Tenn 

Tennessee Logansport, Ind 

ceived and transported by glaciers. The great glaciers of past ages 
had an exceedingly great influence upon the topography of the regions 
which they covered, by their transportation of vast amounts of ma- 
terial. 

The wind in certain regions of the globe is an important agent in the 
transportation of sand and dust. Examples of the action of wind in 
its effect upon the topography may be seen in the great shifting sand 
dunes of the Carolinas and Michigan, and in a number of places in the 
arid portions of the United States and other countries. 

The transportation as effected by stream flow may cause either deg- 
radation or aggradation, depending upon whether the stream is pick- 
ing up and carrying its load of detritus or because of reducing velocity or 



630 


748 


281 


82 


,136 


488 


228 


61 


90 


4 


321 


351 


119 


94 


335 


87 


108 


16 


278 


136 


104 


142 


289 


94 


200 


8 


203 


119 


202 


519 


454 


2,059 


295 


311 


69 


174 


130 


29 


561 


870 


134 


T. 


60 


142 


112 


21 


112 


156 


807 


117 



324 



Geological Agencies. 



volume is unable to carry the load farther, and deposits it, thus building 
up its bed. 

The average amounts of matter in solution and in suspension in parts 
per million carried by various rivers of the United States as deter- 
mined during the years 1906-07 were as shown in Table 36. 5 

154. Results of Erosion. — Table 37 shows the estimate of C. C. 
Babb 6 of the average amount of sediment carried in suspension by 
large rivers of the world to which has been added in the last column 
the number of years required to reduce the drainage area one foot at 
the rate given. 

In the process of erosion lakes are but temporary features ; in the 
lapse of time, their outlets become so lowered that they are drained, 



TABLE 37. 

Discharge and Sediment of Large Rivers. 

Mean an- Sediment Years re- 

Drainage nual dis- Depth over quired to 

River area charge Total an- Ratio by drainage reduce 

sq. miles sec. ft. nual tons weight area in. area 1 ft. 

Potomac 11,043 20,160 5,557,250 1:3575 .00433 2,774 

Mississippi .. 1,214,000 610,000 406,250,000 1:1500 .00288 4,170 

Rio Grande. .. 30,000 1,700 3,380,000 1:291 .00110 10,900 

Uruguay 150,000 150,000 14,782,500 1:10,000 .00085 14,100 

Rhone 34,800 65,850 36,000,000 1:1775 .01071 1,120 

Po 27,100 62,500 67,000,000 1:900 .01139 1,052 

Danube 320,300 315,200 108,000,000 1:2880 .00354 3,390 

Nile 1,100,000 113,000 54,000,000 1:2050 .00042 28,600 

irrawaddy .. 125,000 475,000 291,430,000 1:1610 .02005 600 

and the material carried by the waters of the rivers eventually reaches 
the sea. 

The waves of the lakes and the oceans as they beat against the shores 
erode the cliffs and spread the coarser material along their margins 
(see Fig. 174, p. 315) which in turn is worn by wave action and trans- 
ported by the waves, currents and tides and formed into new deposits. 

The ultimate results of unchecked erosion would be to reduce the 
land surface nearly to sea level. Gradually and more and more slowly 
as the gradient is decreased by erosion, the topographical features of 
the land are reduced and the process would result in a featureless pene- 
plain or base level with just sufficient gradient to discharge the rain 
waters into the sea. These ultimate results from erosion on the land 
areas during the past geological ages have never been more than ap- 

5 Water Supply and Irrigation Paper No. 236. The Quality of Surface 
Water in the United States, R. B. Dole. 

s Science, 1893; Vol. XXI, p. 343; also Eng. News, 1S93, p. 109. 



Results of Erosion. 325 

proximatecl as the conditions of erosion have ever been modified, ac- 
centuated or destroyed by diastrophic movements, upheavals or de- 
pressions of the earth's crust which have either raised the land areas 
more or less and given greater opportunities for further erosion or have 
sunk them nearer or below the sea level where new deposits were per- 
haps laid down over them, obliterating such previous erosive effects as 
may have remained. 

155. Origin and Development of Drainage Valleys. — Wherever 
land surfaces have appeared above the sea, drainage systems have soon 
been established. The original drainage lines have either followed 
natural depressions in the crust or depressions that have resulted from 
lines of structural weakness where normal erosion has been compara- 
tively rapid. 

Extensions of the systems of drainage have resulted from further 
erosion which must normally proceed most rapidly along lines of weak- 
ness caused by weak strata or by other causes which have reduced re- 
sistance and increased erosion, and which proceed slowly when the 
strata are resistant and when other causes of erosion are retarded. In 
this way the original drainage development of a country may, with the 
passage of time, be radically changed and areas drained by one stream 
in which erosion has been held in check, may be seized by the tribu- 
taries of a different stream where erosion is more rapid. 

In the same manner the tributaries of a main stream are pushed far- 
ther and farther toward the divide and frequently even into lands be- 
yond, until a complete system of drainage may effectively be provided 
for thousands of square miles of territory. Such systems have been 
frequently altered and changed by diastrophism, vulcanism and glacia- 
ion. At any one time the larger streams are the result of ages of ero- 
sion and geological change and represent within their length, all stages 
in river growth. 

Where the strata in which a stream develops have approximately uni- 
form resistance, a normal stream bed having a concave profile is de- 
veloped. (Fig. 183). The gradient of the lower portion on account of 
its age and larger flow, has reached a less inclination at or approximating 
its base level. The middle course being younger has a higher gradient 
and a considerable flow, and here maximum corrasion usually occurs. 
The upper portion being of more recent origin and with a small 
amount of flow except at times of flood, has a high gradient. 

Streams with high gradients and consequent high velocities are able 
to transport considerable amounts of sand and heavier rock material 



326 



Geological Agencies. 



































































































































































































































































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Fig. 183.— Stream Profiles. 




Fig. 184. — Vertical Erosion of the Colorado River. 

which corrade their beds and result in comparatively rapid vertical and 
small horizontal erosion. (See Fig. 184.) The work of streams with 
low gradients is largely confined to working over the material in their 



Drainage Valleys 



327 



beds and banks. During periods of floods the excess energy in their 
waters excavate their channels (see Fig. 185) and destroy or rearrange 
their banks (see Fig. 186), and frequently rearrange their local channels. 
(See Figs. 202 and 203, page 340.) With the subsidence of the flood 
stage large amounts of sediment are deposited, old channels are filled 
and excavations in their beds are restored. The study of the work of 
streams is highly important in connection with the design of river con- 
servancy and flood protection work. 



1020- 



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■8 980 

I 970 

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Uj 960 



Aug 18 July 21 April 16 Spring 



< Culmination q[ 

Rise June 23 June, Rise 



July 12 




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Fig, 



O / 2 3 4 5 6 7 

185. — Variations in Cross Section of the Missouri River at Omaha.* 



156. Origin of Falls and Rapids. — When, in the development of a 
river, strata are encountered that have comparatively higher resistance, 
corrasion at such points becomes slow and falls or rapids result. A pool 
is soon formed below the resistant strata as the water with its sediment 
and the matter pushed along the bottom plunges over the resisting de- 
posit onto the yielding strata below ; and where the conditions are favor- 
able, a permanent fall results. In such cases the normal concave profile 
will be modified locally to a greater or less extent. (See profile of the 
Little Colorado River.) In most cases, the ordinary inequalities in the 
strata of the stream bed create a condition of alternate pools and rapids 
which, however, often become comparatively insignificant and are more 
or less obscured when the flow is considerable. 

The resisting strata which produce a falls or rapids may be a local 
inequality of limited extent, such as concretions or boulders, or it may 
be interbeded strata of high resistance. (Fig. 187, A and B, page 1329. ) 
Falls and rapids may result from an intrusive strata such as a dike of 



*J. E. Todd, Bulletin 158, U. S. Geol. Survey. 



328 



Geol 



eologica 



1 A 



gencies 



resistant material which crosses the stream bed (Fig. 187 D) or where 
more Or less horizontal strata of high resistant quality are inclined in 
the direction of or opposed to the flow of the stream. (Fig. 187 C). 




Fig. 186. — Shifting Channel of the Missouri River near Florence, Nebraska 

(see page 187). 

Fig. 188, page 329, shows an intrusive dike across the Kicking Horse 
River near Field, British Columbia, which formerly created a fall at 
that point. The water has at the present time worn a way through the 
dike (see Fig. 189) and the fall is just behind it. The dike is now 
known as a natural bridge. 

Yielding strata below the resistant rock are more rapidly eroded 



Drainage Valleys. 



329 



while strata above the obstruction are in some degree protected by the 
lesser gradient that obtains above the fall. In any event, gradual 
degradation will occur at the crest of the fall which will slowly retire 




Fig. 187. — Falls and Rapids 




Fig. 188. — Intrusive Dike across Kicking Horse River, British Columbia ( see 

page 328). 

upstream as the resistant rock yields to corrasion. Sometimes the re- 
sistant rock is a comparatively thin deposit underlaid by yielding strata, 
as in the case of the Falls of Niagara. 7 (Fig. 190 A and B. ) 

In such cases the underlying yielding rock may be eroded by the corra- 
sion of the waters or disintegrated by weathering, leaving the superim- 
posed resistant strata overhanging and supported only by its transverse 



Rate of Recession of Niagara Falls, G. K. Gilbert. Bui. 306, U. S. G. S- 



330 



Geological Agencies. 




Fig. 189. — Natural Bridge on Kicking Horse River, British Columbia. 



strength. When the unsupported weight is sufficient, the stratum is 
fractured and falls, and the crest of the fall recedes upstream. (See 
Fig. 191, p. 332.) 

Should the resistant strata run out and be worn through, the falls 
rapidly disappear. A rapids first results which is quickly degraded as 
the yielding rock erodes. This nearly occurred at St. Anthony's Falls 



Drainage Valleys. 



331 



on the Mississippi River at Minneapolis where the limestone cap was 
almost totally eroded, in which case the underlying sandstone would 
have been exposed and the fall would have disappeared. It was only 
by considerable labor and expense that the remaining rock was pro- 
tected and the fall thus artificially saved for water power purposes. 

In glaciated areas the whole drainage topography has been modified 
and largely or entirely destroyed, a new topography has resulted, and 
numerous falls and rapids have been developed. In Wisconsin the 
preglacial valleys have been filled with clays, sands, gravels and boul- 
ders for 200 feet or more. On the recession of the glaciers a new 
drainage system began to develop and the country still presents the ap- 




Fig. 190. — Falls of Niagara (see page 329). 

pearance of topographical youth. Even when the new streams partially 
occupy old valleys and flow over materials which are easily eroded, 
erosion is frequently held back by obstructions at the outlets. The 
lower Wisconsin River, for example, flows over a yielding deposit 200 
feet or more in thickness, but the river at its lower end has reached its 
base level on account of the obstruction by the gradient of the Missis- 
sipi River. 

In many places, these new streams in rapidly eroding their chan- 
nels through the yielding drift material, have encountered rock. At 
such points erosion is delayed, while it rapidly proceeds in the stretch 
below the ledge. The result is the development of falls like those on 
the Peshtigo River at High Falls (see frontispiece, upper figure), 
where a drop of over forty feet has been formed. This drop with the 
smaller falls and rapids above, permitted a hydraulic development of 
over eighty feet at this point. (See frontispiece, lower figure.) 

The development of a fall or rock rapids in glaciated country indi- 
cates that the stream bed is not over the thalwag of the preglacial stream 
and is an indication that the lowest outlet past the ledge has not been 



332 



Geol 



eolosica 



1 A 



gencies. 



uncovered by the modern stream. Sometimes the rock outcrop oc- 
curs where the stream has turned through a gap in preglacial hills and 
the channel is then safely protected from radical changes as in the case 
of the Rock River at Rockford, Illinois, where the original channel ex- 
tends to the southward while the modern stream turns through a sad- 
dle in the hills to the southwest. The Mississippi River at Rock Island 




Fig. 191. — Recession of Horseshoe Fall (see page 330). 



Average annual recession 
from parallel 
ordinates from areas 



4.0 


4.4 


6.6 


5.6 


5.3 


5.3 



Period 
Limiting dates years 

1842-1875 33 

1875-1905 30 

1842-1905 63 

Rapids above Moline, Illinois, is also an example of such a change in 
course. Sometimes the rock outcrop which produces the falls is on an 
ancient hillside and in such cases a dangerous condition may result 
under which, with unusual floods the stream may radically change its 
course. Such a change took place in the flood of October, 191 1, at 
Black River Falls, Wisconsin. (See Fig. 192.) A view of these 
falls before and after the flood is shown in Fig. 193, page 334. 
The Black River at this point flows over a rock out-crop on a pregla- 
cial hillside. A dam had been built at this falls, the north end of 
which abutted against glacial drift which was not properly protected. 
The flood waters rising over the abutment readily cut away the drift 
material and the river turned around the end of the dam into the 



Drainage Valleys. 



333 



lower portion of the city, destroying many buildings and much prop- 
erty. (See Fig. 194, page 335). When the river was turned back into 
its course by the construction of a diverting and retaining wall across 
its new channel, the surface of the rock under this wall was found to 
be fifty feet below the rock of the dam site. 

Even in a glacial drift, the boulder clay is so resistant that the 
smaller streams erode it with difficulty and occasionally excavate the 
clay around boulders so large that they cannot be transported by the 
stream. This may finally result in such a resistant mass of boulders 
that a considerable rapids may be developed. (See Fig. 195, 
page 335). 




Fig. 192. — Rock Conditions at Black River Falls. 



The water pouring over the brink of a fall develops considerable en- 
ergy which is expended in impact and eddying in the waters below. 
Erosion is here materially augmented by the rocks, sand and gravel 
carried over the falls by the stream. The bed below a fall is therefore 
frequently excavated to a considerable depth below the stream surface. 
At the Horseshoe Falls of Niagara, the drop of the lower stream sur- 
face is about 170 feet, but the water below the fall is approximately 200 
feet in depth, the bed being eroded in the softer material to this depth bv 
the tremendous energy of the falling waters. (See Fig. 190A, page 
331). The quantity of water which passes over the American side is 
not however sufficient to remove the fallen material from below. (See 
Fig. 190B.) 

In the construction of dams the energy of the stream is frequently 
artificially concentrated in the same manner, and in such cases it is 
important to protect any yielding strata below the dam by a properly 
constructed apron or other protective work. 



334 



Geological Agencies. 




I o 

'•a 
o 

o 



pq 



Drainage Channels. 



335 




Fig. 194. — New Course of River at Black River Falls (see page 333). 




Fig. 195. — Boulder Bed of Wolf River (see page 333). 

157. The Origin of Lakes. — Lakes are of various origins and may 
in general be classified in accordance with their origin as follows : 

A. Diastrophic Lakes. — Caused by accumulations of surface water in the 

depressions which are due to displacement of the crust of the earth. 

B. Crater Lakes. — Formed by accumulations of surface water in the craters 

of jextinct volcanoes. 



336 Geological Agencies. 

C. Glacial Lakes. — Formed in the topographical depressions carved by gla- 

cial action; caused by the obstruction of a valley by a terminal mo- 
raine or by tbe depression left by the melting of the glacier itself. 

D. Bayou Lakes. — Occasioned by the cutting off and subsequent silting up 

of the extremities of a bend in a stream. 

E. The damming of a water course by landslide or similar earth movement. 

F. Obstructions formed across a river by deposition of material as a delta 

at the mouth of a tributary. 

G. Basins due to chemical action such as solution of material to form a de- 

pression in limestone. 
H. Basins excavated by the wind. 

Inland lakes are subject to a further classification, depending in- 
large measure upon the climate in which they occur. Observations 
show that with the proper topographic conditions a low rate of rain- 
fall together with a relatively high rate of evaporation frequently re- 
sults in lakes which can not rise sufficiently to overflow their basins, and 
the continued concentration of the mineral content of the water pro- 
duces a salt lake. Ordinarily lakes that are provided with an overflow 
or outlet are composed of fresh water. The largest inland body of 
water on the globe, the Caspian Sea, is salt, while the second largest, 
Lake Superior, is fresh water. 

The Great Lakes of North America are diastrophic in origin, al- 
though glacial action had much to do with their present form. It is 
probable that the valleys of these lakes were formerly drained by riv- 
ers forming a part of the preglacial St. Lawrence River system (Fig. 
196, page 337). Later, during glacial times, a single lake probably oc- 
cupied the valleys of Lakes Michigan, Huron, and Superior, and Lake 
Ontario was considerably extended. (Fig. 197, page 338). The lake 
system changed its form and outlet at various times during the glacial 
age. On the recession of the glaciers, this system was gradually 
drained, resulting in the system as it now exists. 

A section along the Great Lakes is shown in Fig. 198, from which 
it will be seen that if the lake section was the result of the de- 
nudating effects of river drainage that disastrophism has since pro- 
duced a reverse gradient in the valleys of the three upper lakes. 

Crater lakes are comparatively few and only of local importance. 
The best example of these lakes in America is Crater Lake in Oregon 
which is over six miles in its greatest diameter and has a maximum 
depth of almost 2,000 feet. (See Fig. 199.) 

Glacial lakes are very numerous within the glaciated boundaries of 
the United States. Thousands of these lakes are found within the 
terminal moraine in Wisconsin, Minnesota and other states. These- 



Origin of Lakes. 



337 




Fig. 196. — Preglacial St. Lawrence River Drainage (see page 336). 



«fc?v. 



L ourentide Jce Jfieef 




Fig. 197. — Glacial Lake Algonquin (see page 336), 
Hydrology — 22 



338 



Geological Agencies. 



lakes are frequently of importance as sources of water supply, sites for 
storage reservoirs and pleasure resorts. Some idea of their great num- 
ber may be obtained from an examination of the map of the head- 
waters of the Wisconsin River. (See Fig. 200, page 339.) 



S/ofeSt 



I I ^ *> $ 

^ t$ "S Hi -C; to/re 

J< ia&e M/cfr/gar? $>Lo/re //uron^ § ,J> Er/e 



s s 



§ 5> 







Fig. 198. — Section through the Great Lakes. 




Fig. 199. — Crater Lake, Oregon (see page 336). 

Lakes are sometimes formed in a stream valley by the building of 
obstructions to flow from the deposition of material brought to the 
stream by a tributary. Lape Pepin (see Fig. 201, page 339) on the 
Mississippi, formed by the deposits from the Chippewa River in Wis- 
consin, is an example of this action. The formation of this lake 
caused a retardation of the current of the Mississippi and a deposition 
of the materials conveyed by its waters when it entered the northern 
end of Lake Pepin, and resulted in a local delta formation and the form- 
ation of several minor lakes therein. This delta deposit has filled Lake 



Origin of Lakes. 



339 



Lakes +f 
Marshes i 




Fig. 200. — Intermoraine Lakes of Upper Wisconsin River Valley (see page 

338). 




Fig. 201. — Lake Pepin (see page 338). 

Pepin from a point near the mouth of the St. Croix River to which it 
probably extended at one time, to its present northern extremity near 
Bay City. The Mississippi by the deposits has dammed the outlet of 
the St. Croix to a depth of fifty feet or more, causing the formation of 
Lake St. Croix which is twenty-three miles in length and fifty feet or 
more in maximum depth. 



340 



Geological Agencies. 




Fig. 202. — Lake at Eau Claire, Wisconsin (see page 341), 




Fig. 203. — Bayou Lakes on the Pecatonica River, Illinois (see page 341). 



Origin of Lakes. 



34 



Bayou lakes (see Figs. 202, page 340 and 203, page 340) and bayous 
still connected at their lower ends with the river are often found when 
both or only one of the extremities of a meander which has been cut off 
are filled by deposits. These are of common occurrence in regions of 



/7f wafer u 




Wot/pun 



Chester 




Jf 



JL 



t A 



Le f?ou 



Burnett 
Junction \ 



toV 



. Farmersw'f/e 



> * D * , * 



1 nehoskee 



Mayvi/te 



I 2 3 

5ca/e in Mi/es 



Beai/er Dam 



-SL^£±_^jM/nn\sofa 
Ro///nq Prairie — ■ ffl 

June fy on 



fior/con 



Pig. 204. — Example of a Silting Lake, Horicon Marsh, Wisconsin. 

flat gradients and extensive flood plains. Lakes due to landslides and 
to chemical and wind action are of more limited occurrence and only 
of local importance. 

158. Permanency of Lakes. — Ordinarily the lakes of a humid re- 
gion are relatively short lived. The tributary streams bring in large 
amounts of sediment which are practically all deposited during the 
slow passage of the water through the lake, and the deposits of the re- 



342 



Geological A 



gencies. 



mains of plant and animal life all tend toward rilling the lake bed. 
(Fig. 204). 8 The outlet stream has a continual cutting tendency 
to lower the elevation of the outlet, and thus drain the lake. 
This factor is usually of less importance than the sedimentation be- 
cause of the fact that the outflowing stream usually contains little 
detritus and its eroding ability is correspondingly less. The result of 
these actions is to form an alluvial plain in the lake bed through which 
the stream pursues a sinuous course. When this condition is reached, 
the outgoing stream carries a considerable load of sediment and the 



Cross 5ecl/on -13.70 Miles aooie Oom 




Fig. 205. — Silting of Lake McDonald, Austin Dam, Texas. 

rate of corrasion is accordingly increased so that eventually all traces 
of the lake are removed by the lowering of the stream bed. 

Sedimentation is continually going on in artificial lakes or reservoirs,, 
constructed for the storage of water for irrigation, water power and 
other purposes; and where the material carried by the stream is con- 
siderable the reservoir may soon become silted up and useless. 9 By the 
construction of a dam across the Colorado River at Austin, Texas, a 
reservoir about nineteen miles in length was created. When the dam 
was completed in 1893, this reservoir had a capacity of 83.5 million 
cubic yards of water. In I897 this capacity had been reduced 38 per 
cent by silting, and in 1900 the reduction was equal to 48 per cent of 
the original capacity (see Fig. 205). 

Salt lakes of the arid regions commonly have longer existence than 
those of the humid regions, since sedimentation does not decrease the 



s Physical Geography of Wisconsin, by Lawrence Martin. 
9 See Denudation and Erosion in the Southern Appalachian Region, by L. 
C. Glenn, Professional Paper No. 72, U. S. Geo. Survey. 



Permanency of Lakes. 



343 



volume of water except as the rise it causes exposes a greater area to 
the effects of evaporation. Traces of extinct lakes in the arid regions 
are more enduring than those situated in the humid regions, since the 
erosion and other weathering effected by the rainfall is not so rapid. 

That fresh water lakes existed upon the face of the earth in remote 
geological ages is known by the deposits that were laid down and the 
fossil remains found in these deposits. Lakes more extensive than any 




Fig. 206. — Glacial Lake Agassiz. 



Fig. 



207. — Lakes Bonneville and La- 
hontan. 



now known probably existed in the Cordilleran regions. Sediments to 
the depth of several thousand feet were laid in some of them. Their 
bottoms have since been upheaved to form mountain ranges, and all 
traces of their shore lines have been obliterated. 

Remains of fairly recent lakes in the United States are still quite 
discernible. Three of the largest and best known of these are Lake 
Agassiz, Lake Bonneville, and Lake Lahontan. Figures 206 and 207, 
are maps showing the outlines of these lakes so far as has 
been determined. Lake Agassiz is believed to have been formed by the 
great ice sheet which dammed the drainage of the Winnipeg basin and 
caused the waters to rise, until a southward drainage was opened 
through glacial River Warren, about where the Minnesota River is lo- 
cated at present. 



344 Geological Agencies. 

Lake Bonneville was situated on the east side of the Great Basin in 
the region where Great Salt Lake now lies. The waters from this 
basin overflowed northward through the Snake River into the Colum- 
bia. Its fluctuations are plainly marked by beaches upon the hills. 
(Fig. 208.) 

Lake Lahontan occupied the western side of the Great Basin, and 
is at present represented by Pyramid, Winnemucca, Walker, Carson 
and Humboldt lakes in Nevada, and Honey Lake in California. This 
lake probably had no outlet. Its fluctuations are marked by great de- 
posits of tufa composed principally of calcium carbonate. On favor- 




Fig. 208.— Terraces. Great Salt Lake. 

able localities this deposit may be seen to be over eighty feet in thick- 
ness. 

159. Changes in the Extent of Lands.— The changes that have oc- 
curred and are now occurring in the limits of continental boundaries 
and the extent of the land surface are due to the factors already con- 
sidered. Of these diastrophism, or the rising and sinking of the crust, 
is perhaps the most important. The change in the relative elevation 
of the sea level has also been an important factor. These changes have 
been caused not only by diastrophism but by the extension of the shores 
and the filling up of the lakes and seas by the materials resulting from 
the denudation of the land, and also perhaps during the glacial epoch 
by the extraction of large quantities of water from the ocean by evapo- 
ration and its storage as snow and ice in the great glaciers that have 
from time to time accumulated in polar regions and overrun consider- 
able portions of the Northern and perhaps the Southern Hemisphere. 

A former extension of the eastern coast at some time in the past is 
illustrated by Fig. 209, page 345. which shows the continental shelf 



Changes in Extent of Lands. 



345 




346 



Geological Agencies. 






























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Fig. 210. — The Submerged Valley of the Hudson River (see page 347). 



Changes in Extent of Lands. 



347 



along the eastern United States, the limits of which mark the former 
boundary of the continent. Proof of this is furnished by the fact that 
many of the valleys of the eastern river systems can be traced to the 
edge of this shelf, and it is clear that these valleys could have been 
formed only by atmospheric and eroding agencies during the time that 



Ancient V/l/ioqes 
/ost bu Sea 

1 o Auburn 

2 o tiarfburn 

3 o fiude or Hyfb 

4 o C/e/on or C/outon 

5 o Wifhow 
Hornsea Becft 




Fig. 211. — Changes in the Yorkshire Coast, England. 

this portion of the continent was above sea level. The valleys of the 
St. Lawrence, the Hudson, the Delaware, and the former Chesapeake 
River have been traced far out to sea. The condition of the ancient 
valley of the Hudson, as shown in Fig. 210, page 346, illustrates sim- 
ilar conditions that prevail in many places. The changes in the land 
surface by erosion of the waves and by the deposition of material 
eroded from the exposed surfaces is and always has been of great 
importance. 

Mr. E. R. Matthews states 10 that there is hardly a county of the east 
coast of England that has not had numerous towns and villages de- 



10 Proc. Inst, of Civil Eng., Vol. 159, p. 77. 



348 



Geological Agencies. 



stroyed by the waves during the last few centuries, and he estimates 
this loss at approximately 1,800 acres per annum. Mr. Matthews es- 
timates that the loss along the Yorkshire Coast has been at least nine 
feet per annum, and that the loss since the Roman invasion has been 
approximately as shown in Fig. 211. 

In many cases material accretions are added to the lands by wave and 
current action, for example Dungeness Point on the south shore of 
England is said to have extended seaward over nine feet per annum 
between 1795 and 1850, thirteen feet per annum between 1850 and 




* lamp J 



New land areas 



Mew water areas 
O I Z 3 4 S Mi'/es. 



Fig. 212. — Lower End of the Delta of the" Mississippi River. 



1 87 1, and eight feet per annum between 1871 and 1897, and that in 
consequence the light house had to be shifted three times during the 
past century. 

The extended growth of deltas at the mouths of large rivers is illus- 
trated by Fig. 212, n page which shows the lower end of the Delta of the 
Mississippi River. The Delta receives about 400,000,000 tons of sedi- 
ment every year and is being built out into the sea at an estimated 
average rate of about 300 feet a year. 



11 Mud Lumps at the Mouths of the Mississippi, E. W. Shaw. Prof. Paper 
S5— B, U. S. Geological Survey. 



Literature. 349 

LITERATURE 

GENERAL 

Physiography of the United States, J. W. Powell and others, 1896, American 

Book Company, New York. 
College Physiography, R. S. Tarr & L. Martin, 1917, MacMillan Co., New York. 
Physiography, R. D. Salisbury, 3d Ed., 1913, Henry Holt & Co., New York. 
The Physical Geography of New York, State, R. S. Tarr, 1902, The MacMillan 

Co., New York. 
Physical Geography of Wisconsin, Lawrence Martin, 1916, Bui. No. 36, Wis- 
consin Geological and Natural History Survey. 
Geology, T. C. Chamberlain & R. D. Salisbury, 3 vol., 1906, Henry Holt & Co., 

New York. Vol. 1, Processes and Their Results. 
Geology, Physical and Historical, H. F. Cleland, 1910, American Book Co. 
Text Book of Geology, Part I, Physical Geology, L. V. Pirsson, 1915, John Wiley 

& Sons, New York. 
North America, I. C. Russell, 1904, D. Appleton & Co., New York. 
Geology and Its Relation to Topogmphy, J. C. Branner, Trans. Am. Soc. C. E., 

1898, Vol. 39, p. 53. 
Some Illustrations of the Influence of Geological Structure on Topography, 

R. S. Lyman, Jour. Franklin Institute, May, 1898, p. 355. 
The Interpretation of Topographical Maps, R. D. Salisbury & W. W. Atwood, 

Prof. Paper No. 60, U. S. Geol. Survey, 1908. 

GLACIERS 

Glaciers of North America, I. C. Russell, 1901, Ginn & Co., Boston. 

Existing Glaciers of the United Spates, 5th Annual Report, U. S. Geol. Survey, 
1883-4, p. 309. 

The Rock Scorings of the Great Ice Invasions, T. C. Chamberlain, 7th Annual 
Report, U. S. Geol. Survey, 1885-6, p. 155. 

Glacier Bay and Its Glacier, H. F. Reid, 17th Annual Report, U. S. Geol. Sur- 
vey, 1895-6, p. 421. 

Glacial Sculpture of the Big Horn Mountains, Wyoming, F. E. Matthes, 21st 
Annual Report, U. S. Geol. Survey, 1899-1900, Part 2, p. 167. 

Preliminary Paper on the Driftless Area of the Upper Mississippi River Val- 
ley, T. C. Chamberlain & R. D. Salisbury, 6th Annual Report, U. S. Geol. 
Survey, 1884-5, p. 199. 

Glaciers of Mt. Ranier, G. O. Smith, 18th Annual Report, U. S. Geol. Survey, 
1896-7, Part 2, p. 349. 

The Glacial Gravels of Maine and Their .Associated Deposits, C. H. Stone, 
Monograph 34, U. S. Geol. Survey, 1899. 

The Illinois Glacial Lode, Frank Leverett, Monograph 38, U. S. Geol. Survey, 
1899. 

Drainage Modifications in S. E. Ohio and Adjacent Parts of West Virginia and 
Kentucky, W. G. Tight, Prof. Paper No. 13, U. S. Geol. Survey, 1903. 

Pre-Glacial Valleys of the Mississippi and Tributaries, Frank Leverett, Jour, 
of Geology, Vol. 3, p. 740, 1895. 

The Lower Rapids of the Mississippi River, Frank Leverett, Jour, of Geology, 
Vol. 7, p. 1, 1899. 



350 Geological Agencies. 

EARTH MOVEMENTS 

Earthquakes 

Recent Earth Movements in the Great Lake Region, G. K. Gilbert, 18th Report 
U. S. Geol. Survey, 1896-7, Part 2, p. 595. 

Earthquakes, W. H. Hobbs, 1907, D. Appleton & Co., New York. 

New Madrid Earthquake, M. L. Fuller, Bui. 494, U. S. Geol. Survey, 1912. 

San Francisco Earthquake, G. K. Gilbert and Others, Bui. 324, U. S. Geol. Sur- 
vey, 1907. 

The Charleston Earthquake of August 31, 1886, C. E. Dutton, 9th Annual Re- 
port, U. S. Geol. Survey, 1887-8, p. 203. 

The Kingston Earthquake, C. F. Marvin, Monthly Weather Review, Jan, 1907, 
p. 5. 

The Water Supply of San Francisco, Before, During and After the Earthquake 
of April 18, 1906, Herman Schussler, 1906, Spring Valley Water Co. 

Landslides 

Engineering Geology, H. Rice and T. L. Waters, Chap. VII, Landslides (with 
references), John Wiley & Sons, 1914. 

Landslides and Rock Avalanches, G. E. Mitchell, National Geographic Maga- 
zine, 1910, Vol. 21, p. 277. 

A Suggested Method of Preventing Rock Slides, G. S. Rice, Jour. West. Soc. of 
Engineers, 1913, Vol. 18, p. 585 (with many references). 



The Rivers of North America, I. C. Russell, 1902, G. P. Putnam & Son, New 

York. 
Physics and Hydraulics of the Mississippi River, Humphrey and Abbot, Prof. 

Papers of Corps of Engineers, U. S. Army, No. 13, 1864. 
The Improvement of Rivers, Thomas and Watt, John Wiley & Sons, 1913. 
River Hydraulics, James A. Seddon, Trans. Am. Soc, C. E., Vol. 43, 1900, p. 179. 
The Hydrography of the Potomac River, Cyrus C. Babb, Trans. Am. Soc, C. E., 

Vol. 27, 1892, p. 21, see also Eng. News, Vol. 30, Aug. 10, 1893, p. 109. 
Erosion of the River Banks of the Mississippi and Missouri Rivers, J. A. Ocker- 

son, Trans. Am. Soc, C. E., Vol. 28, 1893, p. 396 and Vol. 31, 1894, p. 26. 
Limiting Waves on Meander Belts of Rivers, H. S. W. Jefferson, National 

Geographic Magazine, Oct., 1902. 
The Atchafalaya River, Some of Its Peculiar Physical Characteristics, J. A. 

Ockerson, Trans. Am. Soc, C. E., Vol. 58, 1906, p. 1. 

Transportation of Solid Matter by Rivers 
The Suspension of Solids in Floiving Water, E. H. Hooker, Trans. Am. Soc, 

C. E., Vol. 36, 1896, p. 239. 
Transportation of Solid Matter by Rivers, Wm. Starling, Trans. Assn., C. E. of 

Cornell Univ., June 18, 1896. 
Methods and Conditions of Transportation of Sediment, Wm. Starling, Eng. 

Mag., November, 1892. 
Silt Movement of the Mississippi, Its Volume, Cause and Condition, R. E. 

McMath, Van Nostrands Eng. Mag., Vol. 28, p. 32. 



Literature. 351 

Erosion of River Beds and Transportation of Detritus, G. K. Gilbert, Eng. 
News, Aug. 19, 1876. 

Lakes, Harbors, Etc. 

Lake Bonneville, G. K. Gilbert, Monograph No. 1, U. S. Geol. Survey, 1890. 

Lake Lahontan, J. C. Russell, Monograph No. 11, U. S. Geol. Survey, 1885. 

The Glacial Lake Agassis, Warren Upham, Monograph No. 25, U. S. Geol. Sur- 
vey, 1896. 

Lakes of North America, I. C. Russell, 1904, Ginn & Co., Boston. 

Geological History of Harbors, N. S. Schaler, 13th Annual Report, U. S. Geol. 
Survey, 1891-2, Part 2, p. 93. 



CHAPTER XIV 

GEOLOGY 

160. Object of the Study of Geology. — The primary object of the 
hydraulic engineer in the study of geology is to determine the structure 
of the earth insofar as such structures will influence his work in rela- 
tion to : 

i. The conditions favorable or adverse to the presence and perman- 
ency of surface or ground waters and their control or disposal. 

2. The discovery, selection and utilization of adequate water sup- 
plies. 

3. The storage and distribution of waters. 

4. Securing and maintaining the qualities of water necessary for 
sanitary and economic purposes. 

5. The reclamation and protection of communities, lands, structures 
and channels from the presence or encroachment of normal and abnor- 
mal waters. 

6. The selection of sites desirable for safe and economical construc- 
tion of dams, reservoirs and protection work. 

The presence of surface waters and the flow of streams depend not 
only on the quantity and distribution of the rainfall but on the geologi- 
cal structure of the drainage area and the amount of water which on ac- 
count of such structure will flow from the area without entering the 
ground, or which will be delivered to streams or lakes from the pervious 
deposits without sinking into the deep underlying strata entirely below 
the bed of the drainage system. 

Navigation, water power, irrigation and water supply engineering 
depend primarily upon the availability of sufficient water either from 
surface streams or underground sources, both of which are largely de- 
pendent upon geological structure. 

The occurrence of surface waters is obvious, but the possibilities of 
the presence of underground waters can be determined only by a knowl- 
edge of the local geological conditions. The presence of such waters 
and their character can often be inferred and often definitely deter- 
mined, without expensive pioneer exploration by a knowledge of the 
geological conditions of the country. 

The practicability of successful storage of waters depends upon the 



Object of Study. 353 

nature of the foundation of the dam or embankments built to retain 
them and the character of the bed and banks of the ponds or reservoirs 
so created. The presence of cracked, fissured, faulted or cavernous 
rocks or of pervious deposits may make such structures impracticable 
either from the expense involved in the construction and maintenance 
of the work necessary to correct the unsatisfactory condition or on ac- 
count of the excessive losses of water due to percolation. The feasibil- 
ity of the distribution of waters through open channels for water sup- 
plies and navigation depends also upon the presence of favorable or un- 
favorable deposits and the condition of the materials through which 
such channels are to be constructed. 

The mineral content of water depends on the mineral character and 
solubility of the geological deposits through which water flows from the 
catchment area to the point of utilization. Its sanitary character de- 
pends upon the conditions encountered in its flow which may be favor- 
able either to the maintenance of organic purity or % to its contamination 
by the wastes of civilization and manufacturing. 

The protection or reclamation of lands from normal and occasionally 
abnormal conditions of flood and drought to which they may be subject 
is largely determined by the topography and structure of such land. 

The foundations of structures and the suitability of sites for safe and 
economical construction and maintenance of dams, reservoirs, canals and 
their appurtenances are largely questions of topographical and geological 
conditions. 

In all cases topographical conditions are more or less evident and can 
be determined in detail by surveys. Geological conditions can be de- 
termined only by expensive exploration and borings, which expense, 
however, can often be largely curtailed by a knowledge of local geology 
and of geological principles. Frequently even extensive exploration 
will not give the information needed without the interpretation which 
can be furnished only by geological knowledge. 

161. Rock Masses and their General Classification. 1 — In general 
all materials forming part of the earth's crust, whether consolidated or 
unconsolidated, are termed rocks. These rock masses may be classified 
into four principal groups : 

i. Archean Rocks, which while probably not parts of the original 
crust of the earth, constitute the earliest known rocks. The Archean 
rocks are believed to be the foundation over which later rocks were de- 



Physiographic Processes, J. W. Powell, p. 11. 
Hydrology — 23 



354 Geology. 

posited and the source from which the sedimentary rocks have been 
most largely derived. 

2. Volcanic Rocks, which result from flows of melted lava that have 
issued from the interior of the earth through volcanoes and volcanic 
fissures. 

3. Sedimentary Rocks, which have been formed in the sea by the dep- 
osition of materials due to the denudating influence of atmospheric 
and hydrological agencies which continually act with destructive effect 
on preexisting rock beds and on the resulting decomposed material dur- 
ing its transportation. These materials have been deposited in more or 
less changed forms and have served to build up new strata which in their 
turn have been lifted up and exposed to like conditions and have served, 
together with the formations already exposed, to furnish the new ma- 
terial for still later deposits. These strata have been laid down in vary- 
ing thicknesses but otherwise are somewhat like the leaves of a book 
with only the upturned edges accessible at the surface while their mass 
in general is largely overlaid by later deposits. 

4. Mantle Rocks, which are the. more or less superficial deposits of 
disintegrated indurated formations produced by the destructive action 
of the atmosphere, of water and of ice, and which either remain a de- 
composed mass over the parent rock or have been transported by vari- 
ous agencies to other localities where they remain a surface deposit of 
soil and subsoil, comparatively loose and unconsolidated. 

162. Historical Geology. — The study of geology has occupied the 
attention of many able and eminent men for many years, and many sec- 
tions of the earth have been studied in considerable detail. From the 
studies of conditions as they now exist, including the arrangement and 
characteristics of the strata, from the geological conditions now under 
process of development, and from numerous data too extensive to men- 
tion, conclusions have been drawn as to various conditions of the past, 
which, if summarized, will give the engineer a concrete idea of the man- 
ner of the growth of the continent, and will assist him in comprehending 
many local hydro-geological conditions which are less readily under- 
stood if examined as isolated and independent problems. The extent 
of certain geological deposits, the physical conditions that obtain therein, 
and the modifications of concomitant hydrographical conditions that 
result therefrom are in this manner more readily understood and ap- 
preciated. The geological deposits of greatest interest to the hydraulic 
engineer are those of sedimentary and glacial origin, for among these 
deposits are those which are of greatest importance as containing waters 



Historical Geology. 355 

available as supplies, and those deposits which from their absorptive 
qualities most greatly influence the flow of streams both from absorbing, 
retaining and supplying waters under favorable hydrological condition. 

The hydrological character of the earlier rocks is not usually such as 
to render them available for water supplies, except through their cracks 
and fissures, which may be of local importance. The absence of absorp- 
tive qualities is, however, frequently of equal importance hydrologically 
on account of its important influence on runoff. 

163. Chronological Order of Geological Time — Division of Strata. 
— From the earliest time the agencies now at work in the disintegration 
and rearrangement of geological deposits have been active in a similar 
manner but intensified at times by more extreme conditions of tempera- 
ture and atmospheric activity. The entire time since scientific observa- 
tions of geological conditions first began has occupied a comparatively 
few years, and the observed changes during that entire period have been 
limited but have served to indicate in no indefinite way the greater 
changes that have occurred in the past. Geological history as deter- 
mined from the strata involves geological activities of millions of years 
and the changes which have succeeded each other have often been wide- 
spread and fundamental. 

The chronological classification of the rock masses has therefore been 
based on the more radical changes which have resulted in : ( 1 ) the 
changed character of the strata themselves, and (2) the markedly dif- 
ferent characteristics in the life existing at the time of formation. 

During all these periods changes more or less complete were taking- 
place in the relative elevations of the rock surfaces both by erosion and 
by disatrophic movements, to both of which are due the contour and limi- 
tations of the existence of the consequent later strata. 

It is important to note that in many cases the deposits of different 
periods shade into each other through transition deposits more or less 
indeterminate, while in other cases the lines of demarcation are more 
obvious and the changes in character more complete. 

The following list includes the most important divisions of geological 
time, arranged in chronological order, the earliest in time occupy the 
base of the column and the remainder occur as they would in their na- 
tural or normal positions. 2 

In no location is the above geological section complete but from the 
occurrence of these strata at various locations the sequence of forma- 
tion has been determined. 



Chamberlain and Salisbury Geology, Vol. 2, p. 160. 



356 



Geology. 



Fig. 213 is a geological map of the United States, showing the gen- 
eral formations so far as they are known to occur at the surface. From 
these outcroppings the strata clip in general in the direction of the later 
deposits, sinking beneath the surface under the more recent formations, 
and can be reached at points below the surface of more recent strata 
only by deep excavations or by the drill. Excavations made on the out- 
crops of geological deposits will in general uncover only formations of 
a still earlier age. 



Cenozoic 



Present \ „ , 

„. . , '. Quarternarv 

Pleistocene ( 

Pliocene ^ 

Miocene 

Oligocene 

Eocene 



Tertiary 



Mesozoic 



Paleozoic 



Upper Cretaceous 
Lower Cretaceous 
Jurassic 
Triassic 

Permian 

Coal Measures — Pennsylvanian 

Sub-carboniferous — Mississippian 

Devonian 

Silurian 

Ordovician 

Cambrian 



Carboniferous 



Proterozoic 



Keweenawan 
Animikean 
Huronian 
Archeozoic Archean 



Algonkian 



Pre Cambrian 



164. The Precambrian Rocks. — At the beginning of the formation 
of the present sedimentary strata, the eafly Archean and Algonkian 
land areas were probably quite limited in extent, in comparison with the 
present exposed continental areas. The approximate boundaries, as 
far as known, and within the present area of North America, are shown 
in Fig. 214A. 

The entire area, deep below the present surface, is supposed to be 
underlaid by Archean rocks of unknown thickness, or by some other 
base rock on which rests the later sedimentary deposits. 

Ages before the formation of the present sedimentary deposits, the 
same processes had resulted in sedimentary deposits which, from the 
lapse of time and by the action of heat, pressure and other agencies, have 
been so changed and metamorphosed as to give many of them character- 
istics quite similar to the earlier Archean formations. 



Surface Formations in United States. 



357 




358 Geology. 

The earliest Archean deposits are the Laurentian rocks, consisting of 
granites, syenites, and allied rocks. Of a later origin are the Algonkian 
deposits, which consist of crystalline magnesium limestone, quartzite, 
slates and schists of the Huronian period, which contain the iron ores 
of Minnesota, Wisconsin and Michigan. The later Algonkian rocks of 
the Keweenawan period, consist of sedimentary rocks, sandstones, con- 
glomerates, and shales, with eruptive rocks containing the copper de- 
posits of the Lake Superior region. 

These rocks are flexed, folded, tilted and metamorphosed, showing 
evidences of upheaval and depression of the earth's crust of great mag- 
nitude and extent. With the exception of the eruptive rocks, most of 
the Algonkian rocks show evidence of sedimentary origin, indicating 
their derivation from a still more remote source, and that they are not 
themselves a portion of the original crust of the earth. 

Subsequent to the formation of the Archean and Algonkian deposits, 
and during the periods of the formation of the earlier sedimentary rocks, 
the central part of North America, including the Great Lake region, was 
occupied by an interior sea, the depth and extent of which fluctuated 
repeatedly. The rise in sea level with respect to the neighboring lands 
at certain times, is believed to have been due largely to the fact that the 
lands exposed to the disintegrating and denuding forces of the atmos- 
phere and of running water, were being reduced to lowlands, while the 
rock waste thus derived from them was being deposited in the sea, 
partly filling the basins. The water thus displaced rose, and even 
though the actual change of level was slight, it was sufficient to cause 
the sea to extend far over the lands on account of their greatly reduced 
elevations. These changes in the relation of land and sea were also 
doubtlessly caused by warpings and dislocations of the earth's crust. 
It is clear that many such warpings have occurred, for strata which must 
at the time of their deposition have been essentially horizontal and con- 
tinuous on the sea floor are now found widely scattered over the lands, 
and in a great variety of warped and folded forms. The reasons for these 
deformations can not be told with certainty. Gravity or the tendency 
of the earth's mass to settle towards its center, has probably caused the 
sinking of certain excessively loaded sections of the ocean floor which 
might have been less firmly supported from beneath than in other locali- 
ties. It is also possible that the cooling of the earth has caused con- 
traction, which has resulted in the outer portions accommodating them- 
selves to the shrinking nucleus by warping or wrinkling. 

Some of the changes that probably took place in the extent of land iv. 



Geological Periods. 



359 




Fig. 214. — Hypothetical Maps of Possible Relations of Land and Sea in Nortli 
America at Various Geological Periods (see page 358). 



360 Geology. 

North America during the formation of the sedimentary strata are in- 
dicated by the hypothetical maps of Fig. 214." 

165. The Upper Mississippi Valley. — To give a clearer idea of geo- 
logical growth, and of the geological structure of the earth, a more de- 
tailed study of some particular locality is desirable. This will enable 
the general features of geological structure to be more clearly under- 
stood than would be possible with the discussion of the larger area of 
the continent, or of the entire United States, where, from the multitude 
of details, the general principles are likely to be obscured. 

For this purpose, the Valley of the Upper Mississippi River has been 
selected, and in the study of the geological history of this territory it 
should be understood that it is but an example of quite similar con- 
ditions which have occurred in all portions of this country and of other 
lands. All lands have had a corresponding geological history, more or 
less varied, but in a general way controlled by similar laws, which 
have resulted in simi'ar general conditions, more or less modified in de- 
tail as the controlling factors have differed in their nature and extent. 

The Upper Mississippi Valley, together with much adjoining terri- 
tory, consisting of the Lake Michigan and Lake Superior basins and the 
valley of the Red River of the North, had a common geological origin 
and history, and, at a comparatively recent geological period, a common 
drainage system, all their waters emptying through various channels 
into the Mississippi River and thence into the Gulf of Mexico, until 
subsequent geological changes so modified the topography as to produce 
the present drainage systems. 

The territory here considered comprises the greater portion of Illi- 
nois, Iowa, Wisconsin and Minnesota, and a small portion of North- 
eastern Missouri and North-western Indiana, and embraces within its 
area much of the richest farming country of the United States, a country 
largely settled, and having numerous thriving and growing communities. 
In the north are forests of pine, and rich mines of iron and copper, while 
in the south are valuable deposits of bituminous coal and fire clay. De- 
posits of valuable building stone are found throughout its extent. It 
contains all the resources necessary for a rich and populous manufactur- 
ing and agricultural development. 

In order to show the details of geologic growths and their effects on 
the present geological and hydrographical conditions, a series of hypo- 



s See Bui. No. 11, Illinois Geological Survey; also Cleland's Geology, and 
Willis-Salisbury Outlines of Geological History. 



Upper Mississippi Valley. 



361 




Pig. 215.- — Hypothetical Maps and Sections of Possible Relations of Land and 
Sea in Upper Mississippi Valley during the Formation of Various Geo- 
logical Deposits (see page 3'60). 



362 Geology. 

thetical maps has been prepared (see Fig. 215) showing the upper Mis- 
sissippi Valley at various periods in its geological history. 4 

166. The Cambrian Period. — At the beginning of the Cambrian 
Period some diastrophic movements produced extended depressions of 
the earth's crust and caused the sea gradually to extend over the low in- 
terior of North America, expanding on all sides, until by the end of the 
period, all the central portion of the continent and most of the western 
and northern portions were submerged. An extensive highland belt 
(The Appalachian Uplift) separated this interior sea from the Atlantic 
on the east and long discontinuous mountain belts in the far west and 
northwest, separated it from the Pacific. On the north a great V- 
shaped land area in Canada (The Laurentian Outcrop), formed at that 
time the main part of the land of the North American continent. Two 
highlands, outliers of the Laurentian land, apparently escaped submer- 
gence : one in the Adirondack region of northern New York, and the 
other in the highlands of northern Wisconsin. Around their subsiding 
borders were spread out in late Cambrian times extensive deposits of 
sand. From the Wisconsin highland region, the sand reached south- 
ward on the sea floor well into Illinois, and now constitutes the Potsdam 
sandstone formation. 5 

During this age the principal part of the upper Mississippi Valley 
(Fig. 215A) was under the sea, which throughout Wisconsin was com- 
paratively shallow and contained many quartzite islands of the Huronian 
formation, which yet rear their heads above the Potsdam outcrop. This 
Potsdam deposit consists mostly of sandstone derived from the broken 
quartz grains of the decomposed granites and allied rocks. These de- 
posits, close to the Archean land, consist of coarse quartzose sand rock, 
very open, porous, and free from the iron, lime and clay, which, in the 
higher strata, are found associated with it. The Cambrian Sea held in 
its depths some of the earliest forms of animal life. Myriads 'of small 
shellfish, the remains of which may be seen in many of the Potsdam out- 
crops, inhabited its waters. 

Although commonly spoken of as a single geological stratum, the Pots- 
dam is by no means homogeneous in texture throughout. During its 
formation a vast period of time elapsed, very many disturbances oc- 
curred, and the circumstances of deposition of the different portions of 
the stratum varied greatly. Those variations were almost or quite as 
great as those that marked the changes to subsequent geological ages. 

The evidence of this, in portions of Wisconsin, is so marked that 



■* See The Hydro-Geology of the Upper Mississippi Valley, by Daniel W. Mead. 
5 Bulletin 11, Illinois Geological Survey. 



Upper Mississippi Valley. 363 

Professor T. C. Chamberlain has classed the Potsdam strata of Central 

and Eastern Wisconsin in the following subdivisions : 

Sub-Divisions of Potsdam Deposit. 

Thickness 
Feet. 

Sandstone ( Madison ) 35 

Limestone shale and sandstone (Mendota) 60 

Sandstone, calcareous 155 

Bluish shale, calcareous 80 

Sandstone, slightly calcareous 160 

Very coarse sandstone, non-calcareous 280 

Total 770 

The thicknesses given are subject to wide variation. As a rule they 
thin out quite rapidly in Wisconsin, northward from Madison, and in- 
crease in thickness to the southward into Illinois. 

Professor W. H. Winchell notes a somewhat similar classification in 
Minnesota. In a deep well drilled in East Minneapolis he found the 
following series of Potsdam rocks. 6 

Section of Artesian Well, East Minneapolis. Thickness 

Feet. 

Sand (Drift) 42 

Blue limestone, Trenton 28 

White sandstone, St. Peter's 164 

Red limestone, Lower Magnesian 102 

Gray limestone, Lower Magnesian 16 

Potsdam: 

White limestone, Jordan 116 

Blue shale, St. Lawrence limestone 128 

White sandstone, Desbach 82 

Blue shale ' 170 

Sandy limestone 9 

White sandstone 130 

Sandy marl, Hinkley 8 

White sandstone 79 

Red marl 57 

Red sandstone 290 

1,069 

Total 1,421 

Although the classification into these sub-divisions is warranted by 
well-defined beds around Madison, Wisconsin, in eastern Wisconsin and 
in Minnesota, yet, owing to the thinning out or disappearance of these 
strata or by the multiplication of sub-divisions, the local variations are 
so great that in many places it is impossible to classify the strata found, 
under any general classification except the general name, Potsdam ; for 
the limits of this formation, as a whole, are well and clearly defined. 

e See Geology of Minnesota, Vol. II, p. 279. 
Hydrology — 24 



364 



Geology. 



As indicated in the foregoing tables, the Potsdam varies greatly in its 
character throughout its extent, not only from shale and limestone to 
sandstone, but also in the character of the sandstone, which is mostly 




Mc. 1I6. — Outcrops of Various Indurated Formations in the Upper Mississippi 
Valley, Drift Mantle Removed (see page 3G5). 

fine-grained, but becomes coarse-grained in its lower strata, and passes 
into a conglomerate near its margin, the shore of the ancient Archean 
land. As may be understood from its physical character, it readily 
transmits the water which it receives at its outcrop, either from rains or 



The Ordbvician Period. 365 

from the numerous streams which flow over its exposed surface, the ex- 
tent of which may be judged from the maps. The outcrops of the Pots- 
dam occupy about 14,000 square miles in central Wisconsin, extending 
in a crescent-shaped tract around the Archean outcrop. (Fig- 216, 
page 364.) Below the later sedimentary deposits it occupies most of the 
area of the Upper Mississippi Valley and furnishes the source of thou- 
sands of private and public water supplies. 

167. The Ordovician Period. — During the Ordovician period the in- 
terior sea continued to expand beyond its limits in the Cambrian period 
through local and temporary oscillations of its floor, and its shores kept 
changing their outline. In northern Illinois, a change from sandy sedi- 
ments to sandy limestones, and finally to pure, fine-grained limestone 
occurred as the period progressed, and indicates that the surrounding 
land areas suffered great reduction under the destructive actions, ero- 
sion and transportation, so that during the middle and late Ordovician 
period, the waters of the interior sea were no longer clouded by river- 
borne sediment, and the deposits made were limited almost wholly to 
shells, corals, and other organic remains. The early Ordovician sedi- 
ments are the Lower Magnesian limestone and the St. Peter sandstone. 
Above them is the Trenton limestone, containing an abundance of fossils 
which indicate that the water was relatively clear, shallow, and rather 
warm. (Fig. 214 B, page 359.) 

In the Upper Mississippi Valley two of these deposits are of consid- 
erable hydrological importance : the Lower Magnesian or Oneota Lime- 
stone and the St. Peter Sandstone. 

The Lower Magnesian is a dolomitic limestone, coarse, irregular in 
stratification, often inter-stratified with shale or sandstone layers and 
limestone breccia, which last, occurring in clusters or heaps, often gives 
the upper surface a billowy appearance and causes it to vary greatly in 
thickness. The variation in thickness seems to be more marked in 
Wisconsin than elsewhere. 

Although undoubtedly cracked and fissured to some extent, it seems 
to be in general free from these disturbances and to offer a quite uniform 
and homogeneous mass to prevent the upward passage of the waters con- 
tained in the Potsdam stratum below it. This stratum is found from 
65 to 260 feet thick through Wisconsin and is from 105 feet to 170 feet 
thick in northern Illinois. It seems to thicken quite rapidly to the south- 
ward, and is found to be 490 feet thick at Joliet, 500 feet thick at 
Streator, and 811 feet thick at Rock Island. A flow of water, which 
may be derived from the underlying Potsdam sandstone, is sometimes, 
found in the softer portions of this stratum. 



366 Geology. 

Over the Lower Magnesian limestone in the Upper Mississippi Valley 
lies a remarkably uniform quartzose sandstone. It is uniform in ma- 
terial and thickness, and quite covers all the irregularities in the surface 
of the underlying limestone, except at some points in Wisconsin where 
it is entirely pinched out and the Trenton limestone lies directly on the 
Lower Magnesian limestone. The average thickness of the St. Peter 
sandstone throughout the territory under discussion is probably about 
150 feet, although in Wisconsin Chamberlain estimates its average 
thickness as only about 80 feet. This deposit is believed to have 
been formed in a shallow sea by the decomposition of the Archean 
and Potsdam rocks. The hypothetical condition of the Upper Missis- 
sippi Valley during the formation of the deposit is shown in Fig. 215B, 
page 361. No fossils have been found in this rock, and its formation 
marked an epoch probably unfavorable to the existence of life. 

This stratum has an outcrop of about 2,000 square miles in Wiscon- 
sin, and also crops out at several points in Illinois along a line of up- 
heaval which passes southwesterly from Stephenson County to the vicin- 
ity of La Salle, bringing the St. Peter to the surface along the Rock 
River at Oregon and Grand Detour, and along the Illinois River from 
La Salle to Ottawa. The Lower Magnesian limestone is also brought 
to the surface at Utica by this uplift. The St. Peter sandstone is an 
important water-bearing stratum, although its outcrop is so low that the 
pressure of its water is usually much less than the water of the Potsdam. 

Although apparently no life existed in this region during the forma- 
tion of the St. Peter sandstone, yet conditions favorable to the exist- 
ence of life again returned, accompanied by geographic changes in the 
relation between the sea and the land, and extensive beds of limestone 
were again deposited. These constituted the- limestones of the Trenton 
group, which may be divided into various substrata more or less distinct 
in character. Of these the Galena limestone is, perhaps, the best known, 
but for the purpose of this discussion the Trenton may be considered 
as a whole, inasmuch as its general character is approximately uniform. 
This deposit through its cracks, fissures and channels furnishes water 
in limited quantities for domestic use. 

Toward the close of the Ordovician period, the Trenton limestone 
deposit was buried by a great sheet of mud over 100 feet in thickness, 
which has since been consolidated into the Hudson River or Cincinnati 
shale. By the time this formation was deposited the interior sea had 
begun to shrink, and the surrounding land to emerge, exposing broad 
coastal plains, from which and across which, the sediment was washed 
into the sea. 



The Silurian Period. 367 

Geographic changes of great extent now occurred. Intense deforma- 
tions in eastern New York added to the width of the Appalachian moun- 
tain belt, while in the Mississippi valley region there was a very exten- 
sive emergence of land, with, however, little or no deformation of the 
rocks. The interior sea shrank to smaller proportions and marine life 
became seriously restricted. These parallel changes of the geography 
and the fauna are the reasons for separating the Ordovician from the 
succeeding Silurian period. 

1 68. The Silurian Period. — With the changes that occurred at the 
end of the Ordovician Period most of the interior of the continent be- 
came dry land, but as the Silurian period advanced, the inter-continen- 
tial sea once more encroached upon a part of the interior of the con- 
tinent. It expanded over Illinois and Michigan and southwest toward 
Arkansas and Missouri, where it was presumably bordered by a land 
area. (See Fig. 214C.) In this interior sea a great limestone forma- 
tion outcrops continuously for more than 1,000 miles from central New 
York to northeastern Iowa and is widely exposed about the Great Lakes. 
It takes its name from the Falls of Niagara, for which the hard lime- 
stone is chiefly responsible. Like most limestone the Niagara Lime- 
stone was originally an organic deposit, made up of an accumulation of 
calcareous skeletons and shells of marine animals, worked over by the 
waves and currents, and ground to a fine calcareous mud. One of its 
distinctive features is its wealth in fossils remains. Evidently, the in- 
terior sea was nearly free from river-borne sediment in most places ; 
hence, it is believed that the surrounding lands were low and the rivers 
sluggish. (Fig. 215 C, page 361.) 

169. The Devonian Period. — At the close of the Silurian period, the 
emergence of large portions of the interior of the continent greatly re- 
stricted the inland sea. Subsidance of the land and expansions of the 
sea were renewed in the Devonian period. (Fig". 214 D, page 359.) By 
me middle of this period, the most of the upper Mississippi and the Ohio 
River were again below the sea. The Devonian occurs as surface rock 
in northwestern Indiana, where it is almost concealed by glacial drift. 
There is a Devonian outcrop near Milwaukee, Wisconsin, and near 
Rock Island, Illinois. 

During the greater part of the Devonian time most of Wisconsin and 
northern Illinois was above sea level, and may have been a part of a 
large land surface stretching south toward the Ozark uplift, of Missouri. 
Near the close of the Devonian period, when the sea again occupied 
much of this region, sands were sifted down into the open joints of the 



368 Geology. 

lower strata, and with it the fossil remains that marked the Devonian 
period in those states. 

170. Carboniferous Period. — The strata of the coal measures are 
the youngest bedrock of the upper Mississippi valley, and are therefore 
the highest rock formation wherever they exist in this region. The 
Pennsylvania system lies at the north margin of the great Illinois coal 
measures, and in most cases is found in isolated patches which lie north 
of the margin of the continuous coal area measures, and are the rem- 
nants of a continuous series which once extended farther to the north. 

The coal measures consist primarily of shales and secondarily, of 
sandstones. Among the shales beds of coal and black seams of carboni- 
ferous matter are common. The unexposed or fresher exposed shales 
are usually blue or drab. They occur in thick massive beds but soon 
weather into thin friable laminae and become lighter in color. 

Sandstone often consists of thick massive beds, but sometimes occurs 
as thin layers interbedded with the shales. The base upon which the 
coal measure rests is very regular in some places ; at the south, it con- 
sists of Devonian limestone, while in the north, coal measures rest on 
the Niagara limestone. 

The probable extent of land and sea during this age is illustrated by 
Fig. 215 D, page 361, which shows the further recession of the sea and 
the consequent limitation of the strata then under process of formation. 

This age ushered in an epoch of life very different from any which 
had preceded it. Its deposits were comparatively local in character, 
and although they have in a general way been correlated, yet there is a 
greater variation in these strata than in those of any preceding de- 
posits. Especially is this true in those of the coal measures proper. 
These deposits seem to have been made in shallow seas, lakes or swamps 
of limited extent, rather than in a broad and deep sea such as those in 
which most of the preceding deposits had been formed. Hence, great 
local variations are observable and the strata have commonly a much 
more limited geographic extent. This age witnessed the formation of 
extensive beds of limestone, sandstone, shales and coal. 

171. Sedimentary Deposits of Later Periods. — The periods briefly 
outlined above, in order to furnish some conception of geologic growth, 
were succeeded in other parts of the country by numerous other more 
recent sedimentary deposits outlined in Sec. 163. These may be of 
great importance in the study of the hydrological phenomena of the 
locality in which they occur. Their consideration in detail is not con- 
sidered of importance in this chapter as the entire subject of geology 



Geological Structure. 369 

must be taken up in much greater detail than is possible in one volume 
in order to give sufficient knowledge for its intelligent application to the 
work of the engineer. 

172. General Characteristics of the Strata. — It should be under- 
stood that lines of exact demarkation seldom exist between the various 
strata. One stratum usually passes gradually into another. Changes 
in the controlling influence which modify the deposition were usually 
not radical and they obtained only gradually. Thus, in passing from 
sandstone to limestone, the upper strata of the sandstone will usually be 
found somewhat calcareous, and the lower strata of the limestone some- 
what silicious. 

A like condition applies to the character of the stratum throughout its 
geographic extent. The conditions at one point may have been such as 
to favor the formation of limestone deposits, while those at a point 
more or less remote may, during the same period, have been favorable to 
the formation of shale. We thus find widely different strata belong- 
ing to the same age. Hence, a stratum may within a short distance 
merge from a sandstone into a limestone, from a limestone into a shale, 
or the reverse, or from a coarse-grained stone to a fine and more im- 
pervious one. Or a stratum may even have been entirely lost by reason 
of a local elevation which raised the rock at that point above the sea 
level, thus preventing deposits, or by the existence of local ocean cur- 
rents which might accomplish the same result. The more widespread 
the conditions controlling deposition, the more uniform is the character 
of the resulting stratum throughout its extent. The character of the 
rock deposit which we may encounter in drilling is often highly problem- 
atic, and it is only by an extended examination of facts as they have 
been found to exist, and by their proper correlation, that we may ar- 
rive at conclusions as to what we must expect in new and untried locali- 
ties. The farther the point in question lies from those where the char- 
acter of the sub-strata is known," the greater is the uncertainty respect- 
ing it. 

173. Modifications of the Strata. — The original extent of the vari- 
ous sedimentary strata of the Upper Mississippi Valley was much 
greater than the present geological map of the region would indicate. 
Hundreds of feet in thickness have been disintegrated and eroded by 
drainage waters. The Hudson River shale, while now encircling Cen- 
tral Wisconsin and Central Northern Illinois as a narrow belt (Fig. 216, 
page 364), undoubtedly once covered a much greater area, as did the 
strata of the Niagara group. The section through Elk Mound shows 

Hydrology — 24 



370 



Geology. 



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CaM. 



Geological Structure. 



371 



the present geological condition, while the prolongation of the limiting 
bed and surface planes of the strata indicate their probable original ex- 
tent. (A-B, Fig. 217.) 

It must also be understood that the sedimentary strata, although orig- 
inally deposited as more or less uniform sheets, each overlying the 
strata below, do not exist in this uniform condition at present ; for many 
disturbances, caused by upheavals and depressions in the crust, (Fig. 
218), have opened cracks and fissures and have caused relative 




Antfc/t'ne 



Suno/ine 




Fati/ted 



7 conformity 





Dip and Strike Monoc/inal ro/d 

Fig. 218. — Some Structural Deformations of Indurated Rocks. 

displacements of the strata (Fig. 219, page 372), amounting in some 
cases to hundreds of feet. The extent of the cracks and fissures caused 
by these disturbances of the strata may be judged by a visit to any 
quarry. Cracks and fissures largely modify the hydrological conditions 
of the various strata, frequently permitting the passage of the waters 
from one stratum to those below or above, and in the latter case giving 
rise to springs. 

In the driftless area of Wisconsin are many sink holes and caves pro- 
duced by the solvent action of underground drainage passing through 
joints and fissures in the Galena, Niagara and Lower Magnesian Lime- 
stone. The sink holes are the entrance to underground drainage 
channels. Some are dry and others contain water, showing the clos- 



372 



Geology. 




1 * 



<6 

I 

(5 
5 



< 
■^ 
* 






Section from the Cafski// Mountains to the Hudson River- (Mather) 




Section across the Vosges and Stack forest fPenck) 




Gener-a/ized Section thru the Uinta /^fountains from North to Sooth (Powe//) 




■Section Cast and West in Centra/ (J fat? ■Shotrinq Numerous feoffs f Duff on ) 

Fig. 219. — Some Structural Deformations Producing Topographical Relief 

(see page 371). 



Geological Structure. 373 

ure or incomplete development of the underground drainage. The 
caves are frequently several hundred feet in length and vary greatly 
in height and width. These caves are limited to the driftless area with 
the exception of a few minor developments near the border of the drift. 
Apparently the glaciers eroded most of the superficial rocks in which 
caves were developed in preglacial times. 

The surface of the underlying Archean rocks slope downward in all 
directions from their outcrop in the extreme northern portion of this 
valley, being about 2,000 feet above sea level at their highest outcrop, 
and perhaps fully as much below sea level at their lowest point. The 
super-incumbent sedimentary strata follows this general slope. The 
Potsdam strata, however, thicken rapidly to the southward, as does the 
Lower Magnesian limestone, so that the higher strata have not as great 
a rate of inclination as the dip of the Archean rocks indicate. (Fig. 
217, C-D.) 

The north and south section illustrates this fact, and shows, moreover, 
that the surface follows the general dip of the strata at present, as it has 
done through all past geological ages ; the outcrops of the older geologi- 
cal deposits being found at the higher elevations. In traveling from the 
original Archean nucleus in any direction the traveler will descend in 
elevation while he ascends in geological succession, passing over each of 
the deposits already described as he approaches the sea level. 

During the ages here briefly reviewed, this territory had gradually 
arisen from the ocean. The carboniferous deposits mark the last age 
of submergence in this area, with the exception of certain minor Cre- 
taceous areas in Northwestern Iowa. 

174. Pre-Glacial Drainage.— With the earliest appearance of the 
land above the sea, the formation of a drainage system began. The 
atmospheric agencies disintegrated the softer portions of the strata and 
carved the rocks into various forms as their varying hardness permitted. 
The drainage waters carried the residuary matter to the sea, thus ex- 
cavating deep drainage va'leys, and forming the later strata by the 
deposition of the material. 

The subsequent alteration of these drainage valleys has rendered it 
al'most impossible to conceive of their early character and extent. The 
hill-tops were higher and bolder than at present. The valleys, deeper, 
more narrow and more rugged, occupied in many cases locations quite 
different from these now occupied. The Lake Michigan valley .was 
then occupied by a river which flowed from the north through the pres- 
ent southern extremitv of the lake, at an elevation some hundred feet 



Geology. 



below the present lake level. This river, with a southwesterly course 
and passing probably not far from the present site of Bloomington, 111., 
emptied its waters into the Mississippi near the present mouth of the 



JETFFRSON 




Fig. 220. — Present and Preglacial Valleys of the Rock River in Southern Wis- 

sin.* 

Illinois River. A light soil covered the valleys and the depressions of 
the hills, furnishing a scant vegetation for the sustenance of animal life. 
The. mammoth and the mastodon, whose descendant, the modern ele- 
phant, is no longer native of this continent, roamed through these early 
valleys, probably a co-inhabitant with primitive man. 



*W. C. Alden, Professional Paper No. 34, U. S. Geological Survey. 



Preglacial Drainage. 



375 



The Mississippi River occupied to a considerable extent its present 
course. To this, however, there are local exceptions, notably at St. 
Paul, La Crosse, Rock Island and Keokuk, where the rock-bottomed 
rapids testify to a diversion from the ancient bed. The river then prob- 
ably drained a much larger territory than at present. It also flowed at 
a level from ioo to 250 feet lower than its present one. It is difficult to 
picture the Upper Mississippi Valley as it then existed, but those who 
are familiar with the driftless area of Wisconsin, north and west of the 
Wisconsin River, including the Dells and country about Devil's Lake, 
can form some conception of the early topography of this whole area. 
This region of Wisconsin has been less altered than any other in the dis- 




Fig. 221. — Comparison of Drainage Systems of Unglaciated (Green County) 
and Glaciated (Walworth County) Areas in Wisconsin. 

trict considered ; yet its valleys, which were then much deeper than now, 
have been deeply filled by the fluvial and lacustrine deposits of the drift 
period. (Fig. 220, page 374.) 

The principal existing streams of this area, and to some extent their 
lateral valleys, have been greatly modified by the subsequent events of 
the Glacial period. A comparison of the present drainage system of 
Green County, Wisconsin, located within the driftless area, with that 
of Walworth County, Wisconsin, within the glaciated regions shown in 

Fig. 221. 

175. The Glacial Period. — From causes not thoroughly understood, 
the consideration of which is unnecessary for the purpose of this chap- 
ter, there followed periods of great cold ; of long winters and short sum- 
mers and perhaps of greater average precipitation than at present, 
which fell as snow over the northern regions and which the heat of the 
short summer was wholly inadequate to melt. The result was the ac- 



376 



GeoloTv. 




Fig. 222. — Hypothetical Maps of Conditions in North America and in the 
Upper Mississippi Valley during the Glacial Periods (see page 377). 



The Glacial Period. 377 

cumulation of vast snow fields, thousands of feet in thickness, similar to 
those which now exist in Greenland and Alaska and in the higher alti- 
tudes of the Alps, the Himalayas and the Rocky Mountains. The 
weight of the superincumbent mass, greatest in depth in the north where 
the summer heat never penetrated, not only compressed its lower layers 
into ice, but forced them to flow in great glaciers to the southward. 
(Fig. 222, A.) Their extent in this direction was limited only by the 
conditions of equilibrium between the melting of the ice mass and its 
motion. The effects of the flow of these vast ice rivers over the irreg- 
ular and deeply marked drainage depressions can be easily understood. 
The rocky hillsides were worn and broken into dust and fragments ; 
huge boulders were torn off and transported hundreds of miles ; and the 
valleys were filled up with the accumulating debris, which was more or 
less sorted and arranged by the sub-glacial waters. At least two epochs 
of glaciation, more or less distinct, can be traced in the Upper Missis- 
sippi Valley. (B and C, Fig. 222.) These have been perhaps the most 
marked causes in the creation of the present conditions, at least in so far 
as they are related to civilized life. To this period the agricultural lands 
of Minnesota, Iowa and Illinois owe their character and fertility, and 
their ability to maintain the population now within their borders. The 
drainage system was altered and the topography was greatly changed 
and re-wrought. Not only were the valleys filled up and the hills cut 
down, but a new class of topographical features was introduced. 

176. Work of Glaciers. — While flowing water can transport only 
debris of a coarseness depending upon the velocity, moving ice will 
transport the largest rock as well as the finest material. The ice deposits 
its heavier material upon melting, most of the finer particles being 
often lost in the floods which result from the melting of the ice. The 
material pushed up or deposited in this manner by the ice is termed a 
"moraine," and when it marks the termination of the ice-flow, a "ter- 
minal" moraine. Such is the Kettle Moraine, which extends across the 
entire territory here considered. When formed on the side of the 
moving ice capes it is termed a "lateral" moraine, and two of these may 
he joined into a "medial" moraine. 

Upon the melting of detached ice masses surrounded by extensive rao- 
rainic deposits about their edges, kettle holes were formed which resulted 
in lakes and swamps. (See Fig. 200, page 339.) 

The streams of water resulting from the rains and melting ice, fre- 
quently cut open channels in the glaciers and sweep into them vast quan- 
tities of material which is there worked over and sorted by the flood, and 



378 Geology. 

deposited as a delta at the end of the glacier, or in long lines between the 
streams of ice, where it is left on the melting of the ice as ridge-like de- 
posits called kames. 

Fig. 222 B is a hypothetical map of the conditions of the Upper Mis- 
sissippi Valley during what is usually termed the first glacial epoch, or 
at the time when the ice had reached its greatest southern extension ; 
while Fig. 222 A shows the same conditions for the continent. The 
limits of the ice are still marked by ranges of hills of morainic material, 
the nature and character of which offer conclusive evidence of its origin. 
Many of the topographical features of the first glacial epoch have been 
greatly modified by subsequent glacial events and by atmospheric and 
aqueous erosion during the time which has since elapsed. The kettle 
holes and lakes have been gradually filled and they are now mostly 
swamps or peat-bogs, and deep lines of drainage have been cut through 
the glaciated area. This process has been greatly aided by the drainage 
waters of the second glacial epoch. During that epoch the extent of 
the ice capes was much more limited than in the first (Fig. 222 C), and 
as its period was more recent, its topographical features are more 
marked. Within the kettle moraine, which marks its limits, are found 
the numerous small lakes which form so striking a feature of Wisconsin 
and Minnesota scenery. 

177. Glacial Recession. — With the recession of the ice capes the 
development of a new drainage topography began. The floods which 
came from the melting ice, inundating great tracts of country especially 
along the Mississippi River, gave rise to lacustrine deposits of consider- 
able depth, known as "loess," a deposit consisting mostly of sand with 
some little clay, and so pervious as to offer little hinderance to the flow 
of drainage waters. The glacial waters had^begun to excavate chan- 
nels for their flow in their earlier deposits, and this process was con- 
tinued in the lacustrine districts as the lacustrine conditions ceased to 
prevail. The old Michigan valley had been filled at the southern ex- 
tremity of the present lake, and the waters being dammed in by the reced- 
ing glacier from the present outlet of the lake, found a passage through 
the present valley of the Illinois River. The waters of Lake Agassiz, 
(Fig. 206, page 343) which was the progenitor of the present Lake Win- 
nipeg, with an area equal, at least, to the combined area of Lake Superior, 
Michigan and Huron, flowed south through the valley of the Minnesota 
River, and through the lake which then existed in a portion of that val- 
ley, into the Mississippi. The other rivers of this area while receiving 
considerable drainage waters from the melting ice, soon lost these waters 



Glacial Drainage. 379 

as the ice receded, and began to act as the drains of their present 
respective drainage areas. 

178. Glacial Drainage. — The hypothetical condition of the country 
at one period in the recession of the glaciers is shown in Fig. 222 D. 
This map shows the location and outline of the southern extension of 
the glacial Lake Agassiz, and also the outline of glacial Lake Minnesota. 
The latter, while shown on the map, was probably either entirely or 
partially drained at this period. The glacial River Warren occupied 
the present valley of the Minnesota River, and to its agency the dimen- 
sions of the present valley are due. This map also illustrates the main 
drainage features existing at this period, at which time the glacial River 
Warren drained Lake Agassiz. The Illinois River drained Lake Michi- 
gan, and through the latter probably Lake Superior, Huron and Erie. 
At a somewhat earlier date, Lake Superior was drained through the 
Brule and St. Croix Rivers directly into the Mississippi, as shown by 
the dotted lines at the western end of the lake ; but, as the glacier re- 
ceded, the outlet from Au Traine Bay to Little Bay de Noquet was 
uncovered, and at the pejiod illustrated by the map the outlet was prob- 
ably at this point. Later the discharge probably took place across the 
peninsula farther to the east. It may, however, be considered doubtful 
whether all of the features shown in Fig. 222 D were contemporary. 

At an earlier period in the recession of the ice cape the Chippewa, 
Black, Wisconsin, Rock and Fox Rivers had received from it a portion 
of their drainage waters, which had undoubtedly outlined the channels 
in which they now flow ; but at the time illustrated in this map they had 
lost these waters and they carried only the flow due to the rainfall and 
drainage of their present drainage areas. 

The vast floods from the melting ice had greatly changed the earlier 
glacial deposits in these valleys. The heterogeneous masses of clay, 
stone and sand were, in many cases, sorted, re-wrought and redeposited. 
As the ice further receded, the present outlet of Lake Michigan was un- 
covered, as was also the Hudson Bay outlet to the valley of the Red 
River of the North. These outlets being at lower elevation than those 
offered by the Illinois and Mississippi Rivers, these rivers also lost the 
drainage which hitherto, as the only outlets, they had been receiving 
from the melting ice capes. In these rivers the results due to the loss 
of the drainage waters were much more marked and the changes in their 
conditions were more radical than in the smaller rivers of this area. 

179. Post-Glacial Drainage. — As the drainage valleys were de- 
prived of waters from the melting ice, their carrying power decreased 



380 



Geology 



and they began to build up their beds, which they had formerly exca- 
vated so as to form a valley commensurate in size and inclination with 
their modern capacities. The local streams, dependent only on local 
rainfall and drainage area, had also begun to develop as the country was 
uncovered by the receding ice. These in the main followed such de- 
pressions as the ice capes had formed. Rarely, if ever, in the glacial 
or local drainage streams, were the earlier drainage valleys closely fol- 
lowed throughout their entire extent. The old valleys having been 
filled, frequently to their tops, it was often the case that the post-glacial 
stream found an easier outlet from valley to valley between the hills 
which formerly separated valleys, than its ancient course. 



One Mi/e 




Fig 223. — Present and Preglacial Valleys of the Mississippi River near Keokuk, 
Iowa (Iowa Geological Survey). 

As the waters cut through the drift, the rocky hillsides were fre- 
quently encountered, and these caused a diminution in the amount of 
cutting by the stream, while the excavation below still went on. In this 
way many falls and rapids have been formed both in the Mississippi 
River and in its tributaries. (Fig. 223, also Fig. 192, page 333.) 

The drift itself, as modified by the glacial waters, possesses largely a 
locally developed stratification, ordinarily somewhat limited in its geo- 
graphic extent. 

The following sections of the drift show its variation in depth and 
general character, which will be seen to be subject to great local differ- 
ences. 

Sections of Drift. 

Bloomington, McLean Co., Illinois. 
Depth 
in feet Material 



10 


Soil and brown clay 


40 


Blue clay 


CO 


Gravel 


13 


Black mucky soil 


89 


Hardpan 


G 


Black soil 


34 


Blue clay 


2 


Quicksand 


254 


feet 



Minneapolis (Lakewood Cemetery 


Depth 




in feet 


Material 


135 


Gravel and sand 


3 


Yellow clay 


74 


Blue till 


36 


Gravel and sand 


8 


Boulders 


256 1 


feet 



Post-Glacial Drainage. 381 

The glacial sheet, which has been described in some detail with refer- 
ence to the Upper Mississippi Valley, and which was there developed 
perhaps to its greatest extent, extended in a broad and irrgular belt 
across North America from the Pacific to the Atlantic, its approximate 
borders being shown on Fig. 222, page 376. 

Within the driftless areas, the ice floods have filled the lower valleys 
with detritus brought down by the flood waters, and have thus modified, 
although to a less extent, the topography of that region. 

The major portion of the glaciated area, outside of the kettle mo- 
raine, is, however, an extended plain, modified by other morainic de- 
posits and by drainage valleys, which have since been somewhat de- 
veloped. At the close of the glacial ages the ancient topography had 
been destroyed and the new was in its infancy, and it is still so slightly 
developed that imperfect drainage is the rule on the plain between the 
rivers. 

The common law of topographical development in the glacial area is 
readily understood. The circumstances of glaciation establish the 
limits of the drainage areas, the waters subsequently flowing from the 
receding ice frequently outlining the location of the streams themselves. 
The flood waters carve their valleys as their quantities and velocities re- 
quire and gradually excavate them until their fall from source to mouth 
is only sufficient to cause the. normal flow of their waters, carrying more 
or less of excavated silt in time of flood. The water has then reached 
its base level, and can go no lower, but works backward and forward 
across the valley, widening and not deepening it. The depth to which 
a stream can excavate its valley is then subject to the controlling fea- 
tures of its point of discharge, which in the case of the rivers of this 
region is limited by the Mississippi River and Lake Michigan. Hence, 
the nearer a valley is located to these outlets, the more marked is its 
character and depth. Few rivers in this area have reached their base 
level, for the time since the glacial age has been too short. The Illi- 
noir River, in its lower course (as has been already mentioned), is an 
exception, the glacial waters having reduced it to a lower grade than is 
suitable for the discharge of its present waters laden with their normal 
burden of silt. Hence, the low lands are flooded and the silt is de- 
posited, gradually raising the bed of the river ; and this process if al- 
lowed to proceed unobstructed, will finally raise the lower river to its 
normal base level. 

By such processes the surface and underlying rocks of the Upper 
Mississippi Valley have been formed. Volumes have been written de- 



382 Geology. 

scriptive of the ages here so briefly reviewed and of the conditions which 
we have been obliged to pass with a glance, and to these the reader must 
turn for further details. Enough has been said, however, to indicate 
the general sequence of events and the general geological condition. For 
practical purposes, each district should be studied in detail and the 
whole subject should be examined with refence to the particular ques- 
tions involved. 

1 80. Hydrological Conditions. — As a source of water supply the 
Potsdam sandstone is one of the most important of the formations in 
the Upper Mississippi Valley, and its character has been examined at 
some length. From this source are derived numerous artesion and 
deep wells, which have been developed throughout the area shown on 
the geological map, Fig. 216, page 364. 

As a source of water, the St. Peter sandstone is next in importance 
in this area. This deposit lies above the Potsdam, being separated from 
it by the Lower Magnesian limestone, and is first encountered by the 
drill. The elevation of its outcrop being less than that of the Potsdam, 
its waters have not usually as great a head and consequently it does not 
as often furnish flowing waters. 

It has already been stated that the drift sheet which covers a large 
proportion of this area contains extensive deposits of sand and gravel 
which frequently offer available sources of water. These deposits are 
sometimes so extended that they may produce many of the phenomena 
observable in wells from the lower strata, such as artesian flows. The 
irregularity in the deposition of these beds of sand and gravel makes the 
drainage area of any particular supply almost impossible to determine. 
Its determination may be, however, a matter of considerable import- 
ance, especially if its source be from districts from which it may receive 
organic contamination. 

In considering the hydrological conditions of the various strata it 
should be noted that all are to some extent water bearing. Even where 
the ratio of absorption is comparatively insignificant, the cracks and 
fissures often play an important part. These strata are saturated to an 
unknown depth, the amount of water varying with the porosity of the 
strata, and with their physical condition as regards cracks and fissures. 
This area, like many others, is marked by an alternation in the deposi- 
tion of rocks varying largely in porosity, strata of high porosity fre- 
quently lying between those comparatively impervious. This varia- 
tion is somewhat equalized by cracks and fissures, but the difference is 
still so marked as to create a great difference in the character of the 
flow. 



Hydrological Conditions. 



383 



The outcrop of these highly pervious strata at the higher elevations in 
the valley gives rise to hydrostratic pressure within the strata, a pres- 
sure which is not wholly equalized by the transfusion of waters due to 
porosity or to rupture. Hence, in the lower portions of the valley, these 
waters often come to the surface with considerable head through natural 
channels as springs, or through artificial channels as flowing wells. 

The existence of water in the strata above renders most efficient aid 
in confining these lower waters of the strata. Without this their immense 




Fig. 224. — Pleistocene Deposits in the United States (see page 386). 

pressures would undoubtedly bring them to the surface. Ordinarily, 
the difference in elevation between the head of the deeper waters and 
that of the ground water is very limited. At Ottawa, Illinois, however, 
it amounts to about 180 feet, and at Aurora, Illinois, to 90 feet. 

181. General Geology and Physiography. — The general outline of 
the outcrops of geological deposits in the United States is shown in 
Fig. 213, page 357. A map showing approximate surface elevations 
of the United States is shown in Fig. 225, page 384, and a map showing 
approximate physiographic divisions of the United States is shown in 
Fig. 226, page 385. More detailed general and local maps can be found 
in the various publications of the United States Geological Survey and 
of the Geological Surveys of the various states. In the literature listed 
at the end of this and the previous chapter, are included only a few of 
the many important works to which the engineer should refer for further 
details on this very important subject. 



384 



Geology. 




Physiographic Divisions. 



385 




Hydrology — 25 



386 



Geology. 



Fig. 224, page 383, outlines the Pleistocene deposits of the United 
States which indicates that in comparatively recent geological times, 
the Gulf of Mexico extended above the mouth of the Ohio River, and 
that a broad belt of comparatively recent sedimentary deposits has been 
formed in the old gulf, which, as the land has gradually risen from the 
sea, has been pushed farther and farther to the southward, very much 
in the same manner that the Mississippi River is now forming new land 




600 



O aOO 400 6O0 800 /OOO /eOO /400 /600 /800^000^^00^400^600^80030003^00 

reef 
Fig. 227 A.- — Plan and Profile of Storm King Crossing of the Hudson River 

(see page 387). 



Upsfr-eam /^ace of Dam ■ 




Fig. 227 B. — Plan and Profile of Borings at Hales Bar Dam (see page 387). 



Investigation of Geological Conditions. 387 

in the Gulf of Mexico. In this way, there has been formed the coastal 
plain which stretches in a broad band from Texas to Long Island, in- 
cluding the entire area of some of the southern states. 

182. Investigation of Geological Conditions. — -In the construction 
of dams, canals, tunnels and other structures depending upon substan- 
tial foundations for their permanency and upon the impervious struc- 
ture of the underlying rocks for their safety or their success in prevent- 
ing underground seepage, no work should be undertaken without ex- 
ploring by excavation or borings. This is especially true within the 
glaciated areas and in regions where the bedrock is known to have been 
largely affected by diastrophic movements of considerable extent. 
(See Fig. 227, page 386.) 

Even where the bedrocks are believed to be essentially in place, bor- 
ings may develop the presence of cracks, fissures, faults or of soft or 
pervious strata, provision for which must be made in engineering de- 
signs in order to assure substantial and safe construction. 

Too great dependence must not be placed upon a few borings espe- 
cially in the drift or in regions where considerable movements have 
taken place, for in both cases the strata sometime vary radically within 
short distances, and the assumption of uniform stratification between a 
few borings widely separated may lead to erroneous conclusions which 
may seriously affect both the estimated cost and the safety of the 
works. 7 

The borings made for the purpose of determining the nature of under- 
lying geological deposits also afford opportunities for hydrostratic tests 
to determine the porosity of the strata and their resistance to the passage 
of water. s 

For the correct interpretation of the results of such borings a knowl- 
edge of the general geology of the regions is essential. In most cases 
where the problems involved are at all complicated, where the expense 
entailed in the construction is considerable or where the results entailed 
by a misinterpretation may be disastrous, geologists familiar with the 



' See Catskill Water Supply of New York, by Lazarus White, Chaps. IV and 
V. Plate 16 shows tentative profiles as deduced from borings for Rondout 
Siphon and at the Kipplebush Gorge, and shows the discovery of faults and 
folds not previously suspected and which would not have been discovered 
without extended exploration work. 

s See Doc. 1202, House of Representatives, 64th Congress, 1st Session. Ten- 
nessee River between Brown's Island and Florence, Alabama (Muscle Shoals 
dam), page 50, Par. 36, "Pressure Tests." See also Eng. News, Vol. 75, 1916, 
page 1229, Investigations for Dam and Reservoir Foundations, by C. M. Saville. 



388 Geology. 

local conditions, or capable of correctly interpreting the superficial 
geology and the data developed by the borings, should be consulted. 

It is probable that if proper borings had been made, the dams at 
Austin, Texas, 9 and at Hales Bar on the Tennessee River 10 would not 
have been constructed at the sites selected, and much trouble and ex- 
pense would have been avoided. 

LITERATURE 

GEOLOGY — PHYSICAL AND HISTORICAL 

Geology, T. C. Chamberlain and R. E>. Salisbury, 3 vols., 1906, Henry Holt and 

Co., Vol. I, Geological Processes and Their Results. Vols. II and III, 

Earth History. 
College Geology, T. C. Chamberlain and R. D. Salisbury, 1900, Henry Holt and 

Company. 
Text Booh of Geology, L. V. Pirsson and Chas. Schuchert 2 Parts, 1915, John 

Wiley & Sons, New York. Part I, Physical Geology, Part II, Historical 

Geology. 
Elements of Geology, Joseph LeConte, Revised by H. L. Fairchild, 5th Ed., 

1910, D. Appleton & Co., New York. 
Geology, Physical and Historical , H. F. Cleland, 1916, American Book Company, 

New York. 
Introduction to Historical Geology, W. J. Miller, 1916, J. Van Xostrand Co.. 

New York. 
Causal Geology, E. H. L. Schwarz, 1910, Blackie & Son, London. 
Outlines of Geologic History with Special Reference to North America. Bailey 

Willis, R. D. Salisbury, 1910, The University of Chicago Press. 
Physiographic Processes, J. W. Powell, Am. Book Co., 1896. 
Hydro-Geology of Upper Mississippi Valley, D. W. Mead, Jour. Assoc. Eng. Sac, 

Vol. 13, 1894. 

ECONOMIC AND FIELD GEOLOGT. 

Economic Geology, H. Ries, 1911, The MacMillan Co., New York. 
Engineering Geology, H. Ries and T. L. Watson, 1914, John Wiley & Sons Co., 

New York. 
Geology for Engineers, R. F. Sorsbie, 1911, Chas. Griffin & Co., London. 
Field Geology, F. H. Lakes, 1916, McGraw-Hill Book Co., New York. 



f> See The Austin Dam, T. U. Taylor, Water Supply Paper No. 40, 1900, U. S. 
Geological Survey; also Report on the Dam and Water Power Development at 
Austin, Texas, Daniel W. Mead, 1917, City of Austin, Publishers. 

io Rock Grouting and Caisson Sinking for Hales Bar Dam, Eng. News, Vol. 
70, 1913, pp. 949 and 1039; see also Eng. Rec. Vol. 59, 1909, p. 470 and Vol. 63, 
1911, p. 641. 



Literature. 389 

Outlines of Field Geology, A. Geikie, 5th Ed., 1912, MacMillan Co., New York. 
Catskill Water Supply of New York, Lazarus White, John Wiley & Sons, 1913. 
Dam and Reservoir Foundations, C. M. Saville. Eng. News, Vol. 75, 1916, p. 1229. 
The Austin Dam, T. U. Taylor, U. S. G. S. Water Supply Paper 40, 1900. 
Report on Dam and Water Power Development at Austin, Texas, D. W. Mead, 

1917, City of Austin, Publisher. 
Rock Grouting and Caisson Sinking at Hales Bar Dam, Eng. News, Vol. 70, 

1913, Eng. Rec, Vol. 59, 1909, and Vol. 63, 1911. 
Tennessee River Between Brown's Island and Florence, Alabama, Document 

1202, House of Representatives, 64th Congress, 1st Session. 
See also Reports of United States Geological Survey and the reports of the 

Geological Surveys of the various States. 



CHAPTER XV 
GROUND WATERS 

183. The Importance of Ground Waters. — Most private and in- 
stitutional water supplies, and many supplies for small towns and even 
for cities of considerable size such as Madison, Wisconsin ; Rockford, 
Illinois ; Memphis, Tennessee ; Austin, Texas, and Savannah, Georgia 
are secured from underground sources. This use of ground waters for 
private and public supplies is due to the apparent and in most cases the 
actual freedom of such waters from the grosser forms of pollution and 
to the fact that in general more satisfactory small supplies and often 
more satisfactory supplies of considerable size can be obtained more 
readily and by less expensive means from ground than from surface 
waters. Ground waters commonly need no treatment to make them 
suitable for domestic and manufacturing uses. Such sources have also 
been extensively utilized for irrigation purposes and occasionally for 
small water powers. 

The low water flow of streams is due entirely to ground waters, and 
conditions favorable to the storage of ground water and its delivery to 
the stream are essential to the maintenance of dry weather flow. 
In humid countries, streams that uniformly dry up in summer are those 
on whose drainage area there is little or no ground water storage. 

The conditions which give rise to underground waters and the con- 
ditions favorable to their flow are also of importance in many hydraulic 
works. Conditions favorable to ground waters may add to the difficul- 
ties and expense of the construction of foundation work and may per- 
mit flows under dams and reservoir embankments and from reservoirs, 
canals and ditches, and thus perhaps endanger the works or at least re- 
sult in a loss of water which may prove more or less serious. 

Ground waters also have important relations to agriculture, and a 
knowledge of these relations and of the flows of water in soil is indis- 
pensable to the engineer in the proper design of drainage and irrigation 
works. 

184. Origin and Occurrence of Ground Water. — All ground waters 
are derived directly or indirectly from the rainfall. The nature of the 
surface on which the rain falls has an important influence on its disposal. 
Such conditions vary from inclined impervious rock or clay surfaces, 
from which practically all rainfall rapidly drains away, through all va- 



Origin and Occurrence of Ground Water. 391 

rieties of texture, porosity and surface covering, to horizontal, pervious 
beds of sand and gravel which under normal conditions imbibe all, rain 
water received on their surface. In general, however ; 

i. A part of the rainfall is evaporated directly into the atmosphere. 

2. A part flows directly into drainage channels as surface flow or 
runoff, and 

3. A part seeps into the soil, subsoil and underlying strata, finally 
reaching an outlet in springs, streams, lakes or in the ocean. 

On account of the saturated condition of the atmosphere during rain- 
storms, evaporation is at such times small in amount compared with 
that which takes place from the soil between rainstorms through capil- 
larity and the action of vegetable life. The evaporation from soil has 
been discussed in Sec. 74, and Fig. 84, page 139, which illustrates evapor- 
ation under different conditions. The evaporation was calculated by 
deducting from the total rainfall the amounts of seepage waters col- 
lected. Fig. 228 is a direct comparison of the seepage and rainfall in 
these same experiments and gives some data on the amount of water 
which passes permanently into the ground water when the soils are well 
drained by underlying pervious substrata, although in the cases noted 
the depths of soil were not sufficient to eliminate entirely the surface 
evaporation losses. (See also Table 7, page 144.) 

In addition to the water received directly from the rainfall it should 
be noted that under some circumstances the ground waters are also aug- 
mented by streams which seep into and sometimes entirely disappear in 
their porous beds (Fig. 232), and by the seepage of irrigation waters 
into the soil. 

All of the materials of the earth's crust, whether loose mantle deposits 
or consolidated rocks, are capable of absorbing water both on account 
of their porous structure and by reason of cracks and fissures. The 
capacity for absorption varies with the porosity of the strata which in 
turn varies with the size and shape of the particles of which they are 
composed and the manner in which they are deposited. Fine material 
may have as great porosity as coarse material, that is the ratio of total 
pore space to volume of the material may be the same in two cases al- 
though the actual sizes of the interstices may be different. Different 
samples of the various geological deposits vary widely in porosity. The 
results of certain determinations of porosity measured by the percentage 
(in volume) of water absorbed are given in Tab!e 38. 



392 



Ground Waters. 




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Fig. 228. — Results of Experiments on 
Soils under Various Surface 



Percolation of Rainfall into Various 
Conditions (see page 391). 



Origin and Occurrence of Ground Water. 393 

TABLE 38. 
Approximate Quantity of Water Which toill be Absorbed by Soils and Rocks. 

Volume of Water Absorbed 
Material per 100 of Material 

Sandy Soil i 45.4 

Chalk Soil i 49.5 

Clay i 50-52.7 

Loam i 45.1-G0.1 

Garden Earth i 69.0 

Coarse Sand i 39.4 

Peat Subsoil i 84.0 

Sand 30-40 

Sandstone 5-20 

Limestone and Dolomite 1-8 

Chalk 6-27 

Granite 03.-.S 

The ground water in general saturates the strata to a depth at which 
the materials are so consolidated by the superincumbent weight that 
cracks, fissures and pores are eliminated. This depth is commonly es- 
timated at from 6,ooo to 10,000 feet but practically the ground water is 
confined to the upper 5,000 feet in sedimentary rocks and to about 500 
feet in crystalline rocks. The strata are in general permanently sat- 
urated to the sea level near the coast and to other higher levels in the 
interior of the country, practically fixed by the surface of lakes, swamps 
or streams. From these more or less fixed water levels the water table 
or ground water surface slopes upward as it recedes from the point of 
discharge. (See Fig. 229, A.) 

The saturation of the strata is not always complete. Many mines in 
both sedimentary and crystalline rocks are dry even far below water 
levels, and sandstones free from water have been encountered in deep 
wells. 2 The water levels of lakes and streams are in general dependent 
upon the ground water level. (Fig. 229, B.) If lakes or ponds are fed 
by streams they may seep into lower adjacent ground waters (Fig. 229, 
C). This condition, however, is unusual except where such bodies of 
water are artificial, under which conditions the lower adjacent ground 
water may cause considerable losses from the stored water. Occasion- 
ally reservoirs or lakes may exist above the general ground water plain 
without serious loss on account of the local underlying impervious 
strata ( Fig. 229, D), and in some cases more than one water table may 
obtain due to local geological structure. (Fig. 229, E.) Water is en- 

1 From Geology of Soils and Substrata, H. B. Woodward, Pub. by Edward 
Arnold, London, 1912. 

- W. L. Fuller, Economic Geology, Vol. 1, page 565. 



394 



Ground Waters. 




*4. ■Section of Long fs/and Showing' f/eva/ion of Ground Wafer 




o .;.- ; Sand and Grove/ ■'■•:o .. ' -°- "':©; 



Q. Lake Maintained by Ground Wafer 




Sancf and Grave/ 



£50 r 



C. Lake Maintained by Stream _, Wafer Seeping info Surrounding So//. 




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,Sha//oyv Wel/s — -, (Pond 




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Mam Water Tai>/e 

77^771 7~/-/~/777~/7 
O./ fy?//e = . . // / 



Perched Wafer Tab/e Ma/nfa/ned by fmpervious Under/ying Strata 

Fig. 229. — Occurrence of Ground Water under Various Conditions of Mantle 

Deposits. 



Movement of Ground Water. 395 

countered in small quantities in crystalline rocks 3 and shales 4 but 
is found more abundantly in limestones, sandstones, and in the sands and 
gravels of glacial deposits and river valleys. 

185. Movements of Ground Water. — The water absorbed by the 
soil passes downward, due to gravity, until it joins and modifies the sur- 
face elevation of the permanent ground water, it then seeps toward 
lower levels through paths of least resistance. The flow of water 
through the strata is governed by the same factors that control hydrau- 
lic flow in canals, pipes or other passages. (Fig. 230, A.) The size 
of the pores or passages in the water bearing material, the length of 
travel (/), the relative height of the source and point of discharge (h), 
and the quantity of water available result in the establishment of an 
hydraulic gradient ( A B) and a resultant flow that remains constant only 
as long as the factors remain unchanged. When the ground water at 
the source rises (B to B,) due to seepage from rainfall or other sources, 
the head (h,), the hydraulic gradient (A B, ), and the flow are increased. 
If through lack of supply the ground water falls (B to B,,), the head 
(h n ) is decreased, and the hydraulic gradient (A B,,) and the quantity 
of flow are reduced. In the same manner the flow of ground water is 
affected by the elevation of the surface of the body of water into which 
it flows. The sudden rise of a river surface (from A A to C C, Fig. 
230, B) due to floods will frequently not only immediately reduce the 
ground water flow from that produced by the normal gradient (AB) 
but will often temporarily stop the flow and sometimes reverse it. In 
such cases the river water seeps back into the pervious banks of the 
stream (CD) until a new gradient (CB) is established. The tide 
influences the flow into the sea in the same manner and necessarily af- 
fects the elevation of the water of wells which draw their supply from 
the same stratum. (Fig. 230, C.) In the same way the discharge of 
springs and flowing wells will increase during the passage of low baro- 
metric storm areas as demonstrated by King (Fig. 230, D). 5 

The ground water surface or hydraulic gradient has a slope propor- 
tional to the resistance of the soil or rock texture to the flow and to the 
amount of water seeping toward the outlet. In gravels and other coarse 



s Underground Waters in Crystalline Rocks, F. G. Clapp. Eng. Rec, Vol. 60, 
1909, p. 525. . 

4 Underground "Waters in Slate and Shale, F. G. Clapp, Eng. Rec, Vol. 59, 
1909, p. 751. 

5 See 19th Annual Report U. S. Geological Survey, 1897-98, Part 2, Princi- 
ples and Conditions of the Movements of Ground Water, F. H. King; also 
Water Supply Paper No. 67. p. 70. 



396 



Ground Waters. 




X? l/ar/af/on of flow and Gradient with Wafer Supply 




B Variarfion of Flow and Gradient yvifh River Heights 

■JulyS Ja/ y /0 . July II Ju/y/2 




C effect of Tides on Fl evafion of Ground Wafer { l/eatch) 

Wednesday Thursday Friday 

12 2 4 6 8 10 M 2 4 6 8 /O 12 2 4 6 8 /0 M 2 4' 6 8 10 12 2 4 6 8 /OM 

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29.5 

23.0 

O effect of Baromefnc Pressure on Discharge of Spnnas and Wells, ftfing) 

Fig. 230. — Gradients and Elevations of Ground Water as Affected by Various 
Conditions (see page 395). 































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Movement of Ground Water. 



397 



materials the water moves freely and the inclination of the water sur- 
face is comparatively small, while in materials of close texture the 
gradient must be considerable to produce movement. 

In their flow from the line of the drainage area to the stream the 




Diagram Showing Levef of Ground Wafer During Spring Reriocf and ifs fSffecf 
on Var/ous Surface Condifions. 




Diagram Shoyving Leref of Ground Wafer During Summer Period and Change 
of Various Surface Condifions. 

Pig. 231. — Normal Conditions of Ground Water during Wet and Dry Periods 

(see page 398). 




■Scale of 'Miles 
o 10 20 JO 



Fig. 232. — Deltas of Disappearing Streams (see page 399). 



398 



Ground Waters. 



seepage waters commonly encounter differing degrees of resistance due 
to changes in porosity and size of soil grains even in the same stratum, 
hence the gradient is seldom constant except for short distances where 
uniform conditions prevail. Due to irregularities in surface and sub- 
surface conditions the hydraulic gradient recedes from or approaches 






Gra v/ty 


Spring 


c 








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Spring due to Fautf or Fissure. 




Spr/ng from fissured flock 



Spring from Cavernous f-fock 




Submarrne Spring from Pervious Stratum fnferm/ttant Spring 

Fig. 233. — Geological Conditions which give Rise to Various Classes of Springs 

(see page 399). 

the surface and gives rise to various phenomena illustrated in Fig. 231. 
When the water plain or hydraulic gradient reaches or passes above the 
surface the ground water causes springs, streams, lakes or swamps 
(Fig. 231, A), which during dry weather may become partially or en- 
tirely dried up when the water plain falls below the surface at the 
locality where it formerly existed. (Fig. 231, B.) In some cases the 



Movement of Ground Water. 



399 



ground water by reason of other and lower outlets may fall below the 
beds or adjacent streams in which case the streamflow will be decreased 
by seepage into its bed and banks. This is often the case in Eastern 
rivers when sudden floods raise the stream surface above the ground 
water level as noted above and is a phenomenon of common occurrence 
in the West where desert streams fed from the mountains flow into 
plains having small rainfall and low ground water. In some cases 
under such circumstances the streams are entirely lost by sinking into 
the plains after leaving their mountain channels. (See Fig. 232.) 




Fig. 234. — The Thousand Springs, Snake River Canyon, Idaho. 

In many cases ground waters seep through pervious deposits which 
lie below comparatively impervious beds on which they produce an 
upward hydrostatic pressure due to the head at their source less the head 
lost by resistance of flow. Where such waters encounter cracks, fis- 
sures or wells through the overlying deposits, they rise through such 
openings and if the hydrostatic pressure is sufficient may appear at the 
surface as springs or flowing wells. 

186. Springs. — When the hydraulic gradient of the underground 
water passes above the surface at any point (Fig. 231, A), and when the 
water bearing strata also reaches or connects with the surface, springs 
are formed. (Fig. 233.) Springs are sometimes produced by surface 
outcrops of impervious strata overlaid by pervious water bearing de- 



400 



Ground Waters. 




SaBTO/v 3f>GjNaL 



« 




Fig. 235 A. — Fault Zone near Austin, Texas (see page 401). 

posits (Fig. 233, A), or by the occurrence of surface outlets from 
cracked, fissured or cavernous rocks. (Fig. 233, C.) The open texture 
of the lava rock on the side of the Snake River Canyon in Idaho has 
given rise to the series of springs shown in Fig. 234. Sometimes the 
hydrostatic pressure raises the underground waters to the surface 



Springs. 



401 



through cracks, fissures or fault lines (Fig. 233, B). Springs of large 
capacity are often found along fault lines where the faults intersect 
deep lying water bearing rocks. Such a condition is found near Austin, 
Texas (Fig. 235), where an extensive fault zone exists. Numerous 



/Qusf/n Cha/k 

Buc/erCShoa/Oh S ■ 
Limestone ' 




Feet 
r/000 



fagteford Sha/es 
Dei Rio C/ays 
■Fort Worth Limes tone 




Traris k&ak 
formation 

Miles 

Fig. 235 B. — Geological Section Through Fault Zone near Austin, Texas.* 




Fig. 23G. — Barton Springs from Fault, Austin, Texas, 
springs are found in this vicinity the largest of which is Barton Springs 
on the south side of the Colorado River (Fig. 236). This spring flows 
through fissures in the rock bed and banks of Barton Creek and has an 
average flow of about fifteen cubic feet per second and will probably be 
utilized as a water supply for the City of Austin. 

The cracked, fissured and pulverized rock of one of these faults pass- 



*Geologic Atlas of the U. S., Austin Folio, R. T. Hill and T. W. Vaughan, 19.02 
Hydrology — 26 



402 



Ground Waters. 



ing under the bed of the river at the dam site above Austin was un- 
doubtedly the cause of the failure of the dam at that place in 1900 and 
of much of the trouble in rebuilding that structure. 




f_= Approximate Strike Lines Soft 
=£T= and Cavernous Strata 



Ponds and S/nks in Limestone Strata 




iOOOO 



300O0 



40000 



£0000 
Distance in /^eef 
SLTCrtOiV AB 
Fig. 237. — Map and Section near Sheffield, Albama, Showing Conditions which 
give Rise to Disappearing Streams and to Springs. 

Springs often result from the flow of water through the passages 
in cavernous rock which outcrop at or above the surface. (Fig. 233, D.) 
In general, the formation of caverns by solution is limited to the rock 
mass above the outlet water level although the rock structure may occa- 
sionally produce lower lines of flow and consequent cavernous condi- 

g Austin Dam, T. U. Taylor, Water Supply Paper No. 40, 1900, also Report 
on the Dam and Water Power Development at Austin, Texas, Daniel W. Mead, 
City of Austin, Publisher. 



Springs 



403 



tions far below the outlet water levels. In other cases cavernous condi- 
tions may have been produced in the rocks of valleys that have later 
been filled with glacial, lacustrian or fluvial deposits, or disastrophic 
movements may have lowered the cavernous rock far below the present 
water plains. 

Numerous springs of this class occur in most limestone regions. The 
exposed beds of soluble limestone in Northern Alabama near Sheffield 
(Fig. 237) have developed many cavernous channels. Into one of these, 
Pond Creek, draining about 35 miles of surface area, disappears. The 




Fig. 238. — Outlet Creek from Tuscumbia Springs near Sheffield Alabama (see 

Fig. 237). 

development of cavernous conditions in another stratum gives rise to 
Tuscumbia Springs (Fig. 238), one of the largest springs in Northern 
Alabama. 

Springs from cavernous stone are sometimes intermittent on account 
of peculiar formations. In general, such results are produced by the 
formation of a collecting cavern within the rock together with a syphon 
outlet channel (Fig. 233, F) in which case the water begins to flow when 
the cavern fills to the top of the outlet channel and ceases to flow when 
the supply in the reservoir or cavern is exhausted, which action is re- 
peated as the reservoir alternately fills and empties. Frequently in- 
clined pervious strata are exposed by the erosion of the overlying rock 
by streams, lakes or the ocean and numerous surface and submarine 
springs result. (Fig. 233, E., page 398.) 



404 



Ground Waters. 



187. Artesian Conditions. — Early wells drilled into the deep under- 
lying strata in the Province of Artois, France, produced flowing waters 
at the surface. Similar conditions have since been discovered in num- 
erous parts of the world and such conditions and the wells which de- 
velop them have been called "artesian" from the place of their first de- 
velopment. 

In order to produce flow at the surface the hydraulic gradient of the 
underlying water bearing deposits must pass above the surface, other- 
wise the water will simply rise in the well to the local elevation of the 
gradient. (Fig. 239.) The term artesian is, however, commonly applied 









m— — 11 m r'T,'- -'' 



-^ 



M 



- ? -- 



'Crc/sfalline Rock ~ 
11-11 = 11=11=11=. n= ( , 



•4j, 




- m - 



Fig. 239. — Section Showing Artesian Conditions and Relations of Flowing and 
Non-Flowing Wells to Hydraulic Gradient and Surface Elevation (Fuller). 

to both rising and flowing wells and also to springs occurring through 
cracks, fissures and faults. (Fig. 233, B.) 

The leading prerequisite conditions on which artesian flows depend 
are given by Chamberlain 7 as follows : 

1. A pervious stratum to permit the entrance and the passage of the 
water. 

2. A practically water-tight bed below to prevent the escape of the 
water downward. 

3. A like impervious bed above to prevent escape upward, for the 
water, being under pressure from the fountain head, would otherwise 
find relief in that direction. 

4. An inclination of these beds, so that the edge at which the waters 
enter will be higher than the surface at the well. 



' The Requisite and Qualifying Conditions of Artesian Wells, T. C. Cham- 
berlain, Fifth Annual Report U. S. Geological Survey, 1884, p. 131. 



Artesian Conditions. 



405 



5. A suitable exposure of the edge of the porous stratum, so that it 
may take in a sufficient supply of water. 

6. An adequate rainfall to furnish this supply. 

7. An absence of any (easy) escape for the water at a lower level than 
the surface of the well. 

For large flows the waterbearing material must be coarse and porous 
or the thickness must be great and the outcrop must be of large area and 
the rainfall ample. 




Fig. 240. — Map Showing Principal Artesian Areas of the United States. 

The artesian wells of Denver formerly provided a large surface flow 
in the spring and early summer when the snow was melting from the 
foothills, but these wells decreased or ceased to flow during the dry 
periods of the summer. The numerous artesian wells in the Upper 
Mississippi Valley (for geological section see C D, Fig. 217, page 370), 
especially those derived from the Potsdam Sandstone show no seasonal 
variations in flow due to the extended outcrop of the Potsdam in North- 
ern Wisconsin (about 14,000 square miles, see Fig. 216, page 364). The 
principal artesian areas in the United States are shown in Fig. 240. 
Geological sections which show the conditions that give rise to such 
wells are given in Fig. 241 for the Dakotas (A), along the Atlantic 
Plains (B), in Eastern Texas (C), and in the San Joaquin Valley (D). 
Numerous local artesian conditions are developed in the drift in Wis- 
consin, Illinois, Indiana and other localities, and many minor artesian 



406 



Ground Waters. 



4O00 7TZ 




fJ- Cross Section through South Da KoTa Artesian Basin. ( Darton.) 



• J 



Atlantic Ocean 




| 400 
\ ZOO, 



^^Wmwm 



^§^m^mmMm 



\$^m^$$. v xxxx MTOn> 



G- [deal ' •Section Showing Artesian Conditions at Ft. Worth, Texas. 



I 
tzooo 



Brewster — iMerrill r-Tu/are , 
Baird— \ I I if arret -, r Visalia 




D-Ideal*5ectior7,3anJoaquin ]/alley through Tulare Lake. (GrunsHy) 

Fig. 241. — Geological Sections Showing Various Artesian Conditions in the 
United States (see page 405). 



Underflow of Streams. 



407 



areas occur locally in various points of the United States, especially in 
the lower lands of river valleys. 8 

188. The Underflow of Streams. — Many streams flow over beds of 
sand, gravels or other pervious materials such as lacustrine deposits and 




Sec f/o/-? ar 6> c 

Fig. 242. — Map and Section Showing Ground Water Conditions in the Gila and 
Salt River Valleys. After Lee. (See page 408.) 

those which have been deposited in older and deeper valleys by glacial 
action, by the work of former streams or by the present streams where 
conditions have changed their work from degradation to aggradation. 
These deposits are frequently very extensive and sometimes afford op- 



s Water Supplies of Wisconsin, S. Weidman and A. R. Schultz, Bui. No. 35, 
Wis. Geol. and Nat. Hist. Survey, 1915, p. 88. 

The Water Resources of Illinois, Frank Leverett, 17th An. Report U. S. 
Geological Survey, 1895-96, Pt. 2, p. 78. 

Water Resources of Indiana and Ohio, Frank Leverett, 18th An. Report 
U. S. Geological Survey, 1896-97, Pt. 4, p. 480. 



408 



Ground Waters. 



portunities for securing abundant water supplies at points far distant 
from the stream channel. The underflow of the Salt and Gila River 
Valleys in Arizona (Fig. 242) is extensively used for the irrigation of 
lands both inside and outside the United States reclamation project 
boundaries, some of these wells furnishing (by means of pumps) sup- 
plies of four cubic feet per second (Fig. 243). Many supplies of cities 




Fig. 243. — One of the Wells of the Southwestern Cotton Company in the Gila 
Valley. Four Cubic feet per Second Pumped from Ground Water. 

are taken from similar sources. The water supply of Wichita, Kansas, 
is derived from the underflow of the Arkansas River and provides an 
adequate amount of water for that city when the river bed is dry and the 
ground water surface of the underflow is drawn down several feet below 
the river bed. (Fig. 244.) In many cases where the old stream valleys 
are filled with sands and gravels, the presence or absence of streamflow 
is simply a question of the elevation of the general ground water gradient 
above or below the stream bed. In other cases, when the present beds 
are more or less impervious, the streamflow and the underflow are 
independent both in character and direction of flow. 



Temperature of Ground Water. 



409 



189. Temperature of Ground Waters. — It has been shown (see Fig. 
14, page 48) that the temperature of the earth below the surface is 
not subject to as great a range of temperatures as air or surface waters. 
In consequence of this even the higher ground waters are comparativly 
cool in summer and warm in winter. There is also a considerable in- 
crease in temperature from the surface downward amounting in gen- 
eral to about one degree for each 50 to 100 feet. The U. S. Geological 
Survey measured the temperature in the deep well at Wheeling, West 
Virginia with the results shown in Table 39. 




Fig. 244. — Sand Bed of the Arkansas River at Wichita, Kansas, during Low 

Water (see page 408). 







TABLE 


39. 




nderground Temperatures at Different Depths in the 


Well at Wheeling, 






West 


Yir 


ginia. 






Temperature 






Temperature 


Depth Feet 


Fahr. Degrees 




Depth Feet 


Fahr. Degrees 


100 


51.30 






2,990 


86.60 


1,350 


68.75 






3,125 


88.40 


1,591 


70.15 






3,232 


89.75 


1,592 


70.25 






3,375 


92.10 


1,745 


71.70 






3,482 


93.60 


1,835 


72.80 






3,625 


96.10 


2,125 


76.25 






3,730 


97.55 


2,236 


77.40 






3,875 


100.05 


2,375 


79.20 






3,980 


101.75 


2,436 


80.50 






4,125 


104.10 


2,625 


82.20 






4,200 


105.55 


2,740 


83.65 






4,575 


108.40 


2,875 


85.5 






4,462 


110.15 



410 



Ground Waters. 



These temperatures may be compared with those of the deep well 
near Berlin, Germany, which is 4170 feet in depth and has a surface 
temperature of 47.8° and a bottom temperature of 118.6 , and with the 
well at Leipsig, Germany, 5,740 feet deep with temperatures at the top 



TABLE 40. 
Temperatures of Deep Well Waters. 



Location of Well 



Rockford, 111 

Galena, 111 

Oak Park, 111 

Ellendale, N. D. ... 

Redfield, S. D 

Huron, S. D 

Yankton, S. D 

Jamestown, N. D. 
St. Augustine, Fla. . 

Alamosa, Colo 

Canon City, Colo.. .. 

Denver, Colo 

Denver, Colo 

Guntersville, Ala. . . 
Arkansas City. Ark. 

Loyalton, Cal 

Santa Clara. Cal. . . 

Oglethorpe, Ga 

Keokuk, la 

Richfield, Kan 

Louisville, Ky 

Elkton, Md 

New Orleans, La. . , 

Alpena, Mich 

Winona, Minn 

Scranton, Miss 

Louisiana, Mo 

Miles City, Mont. . . . 

Omaha, Neb 

Sierra Valley, Nev. . 

Longport, N. J 

Ashland, Pa 

Charleston, S. C. ... 
Knoxville, Tenn. . . 

Ft. Worth, Tex 

Galveston, Tex 

Reedville, Va 

N. Yakima, Wash. . . 
Green Bay, Wis. . . . 





Tem- 




pera- 


Depth 


ture De- 


of Well 


grees F. 


1320 to 1996 


60 


1509 


49 


2780 


64 


1087 


67 


960 


68 


863 


60 


600 


62 


1576 


75 


1400 


86 


1000 


75 


1600 


90 


500 


50 


350 


56 


1006 


60 


552 


72 


1000 


130 


600 


60 


490 


62 


2000 


65 


370 


66 


1900 


57 


490 


45 


1200 


68 


650 


52 


478 


54 


774 


74 


1275 


64 


456 


57 


1065 


62 . 


1132 


Hot 


803 


66 


1830 


54 


1970 


99.5 


2100 


57 


3250 


140 


1365 


84 


680 


78 


650 


71 


950 


53 



Reference 



Eng. News, Vol. 21, 1889, p. 326, 

1 

-Eng. News, Vol. 21, 1889. 
Eng. News, Vol. 27, 1892. 



'1 



1-U. S. G. S. Water Supply Paper 51 



U. S. G. S. Water Supply Paper 61. 



Temperature of Ground Water. 



411 



and bottom of 51. 9 and 135.5 ° respectively. On account of these con- 
ditions deep well waters are usually much warmer than the shallower 
ground waters, as shown in Table 40. 

In certain regions thermal springs are found which are sometimes of 
boiling temperatures. Some of these derive their temperature from the 
great depths to which the seepage waters have previously percolated 
through fissures. In other cases the waters are heated by chemical ac- 
tion, while in volcanic regions waters are heated to high temperatures at 
comparatively shallow depths by the presence of uncooled lava. There 
are about 3,000 springs of this latter class in Yellowstone National Park. 



TABLE 41. 

Qualities 0/ Water Collected During a Rainstorm, at Rothamsted, England.^ 

(Parts per million) 





Total 
Solids 


Carbon 

in 
Organic 
Matter 


Nitrogen as 




Time 

of 

Collection 


Organic 
Matter 


Am- 
monia 


Nitrites 

and 
Nitrates 


Total 

Ni- 
trogen 


Chlor- 
ine 


3:00 P.M. 
4:30 P.M. 


40.8 
29.4 


0.93 
0.62 


0.18 
0.19 


1.07 
0.37 


0.18 
0.13 


1.43 
0.69 


1.0 

0.8 



190. The Qualities of Ground Water. — No water is found in a state 
of chemical purity in nature. The rain falling through the atmosphere 
takes up various floating matters and absorbs various gases from the air. 
Its quality improves in the later part of the storm after the air has been 
partially cleansed by the earlier rainfall. (See Table 41.) 

When it reaches the ground, the rain water as it runs over the sur- 
face dissolves, erodes and carries away in solution and in suspension 
some of the various materials with which it comes in contact. In this 
way the streams receive the washings from farm yards and fields and 
carry away silt, sand and organic matter to the rivers and the sea. In 
the same manner the water also carries similar matter into cracks and 
fissures of the rock, but as it seeps into the soil and sand, the coarser 
materials in suspension are left on the surface and only the finer organic 
and mineral matter and the matter in solution are carried into the 
ground. As the water flows through the soil and underlying forma- 



9 Journal of the Royal Agricultural Society, 1847, p. 257. 



412 



Ground Waters. 



tions, the matter in suspension is rapidly removed if the strata are fine 
material, but the moving water constantly adds to its burden of matter 
in solution and becomes more highly mineralized the more soluble the 



47 




Fig. 245. — Average Mineral Content in Parts per Million of Surface and Rock 
Wells in Wisconsin. After Weidman and Schultz. 

material of the strata with which it comes in contact and the longer and 
farther it flows. 

Water from the cracks and fissures of the comparatively insoluble 
crystalline rocks contains only a small amount of matter in solution and 
is termed "soft water." The mantle and sedimentary rocks contain 
much soluble matter and the waters from such deposits are more highly 
mineralized the farther they are found from their source. As in gen- 
eral the deeper rocks in any section appear at the surface and absorb the 



Qualities of Ground Water. 



413 



rainfall at a greater distance from that section, the deep waters are in 
general more highly mineralized than those from lesser depths. The 
progressive increase in mineral content of the ground water in propor- 
tion to the depth and travel is shown in the map (Fig. 245) and section 
(Fig. 246) of Wisconsin, and in Table 42 which includes also the deeper 
waters of Iowa. 10 In Iowa deep wells are defined as those more than 
700 feet in depth. 




-J500 



Fig. 246. — Geological Section through Wisconsin and Average Mineral Content 
of Surface and Rock Wells. After Weidman and Schultz. 

TABLE 42. 
Showing the Relation 0/ Depth to Mineralisation of Underground Water in 

Wisconsin and Iowa. 



Approximate Depth 






of Underground 




District 


Water or Thick- 


Average Mineral Content 




ness of the Water- 


in Parts per Million 




bearing Strata 






100 to 200 Feet... 


Surface Deposit Wells 121 




400 to 800 Feet... 


Rock Wells 135 




Surface Deposit Wells 224 




800 to 1600 Feet.. . 


Rock Wells 216 


Southwestern Wisconsin . . 


Surface Deposit Wells 330 






Rock Wells 339 


Northeastern Iowa 


1600 to 2000 Feet... 


Shallow Wells 388 

Deep Wells 351 


Central Iowa 


About 3000 Feet. . . 


Shallow Wells 873 




Deep Wells 1759 


South Central and South- 






western Iowa 


About 4000 Feet.. . 


Shallow Wells 1587 




Deep Wells 3657 







10 Water Supplies of Wisconsin, by Samuel W. Weidman and A. R. Schultz. 



414 



Ground Waters. 



The character of the mineral content of underground waters depends 
entirely upon the chemical character of the strata through which they 
flow. (See Table 43.) The waters of the Potsdam Sandstone of the 
Upper Mississippi Valley (see Table 44) are more largely charged with 
the bicarbonates of lime, soda and magnesia, with minor quantities of 



TABLE 43. 

Analysis of Residues of Various Spring Waters in the Upper Mississippi 
Valley, Grams per U. S. Gallon. 



Compound 


Elgin, 

111. 
'Zoman 
Spring 


Cook Co., 

111. 

Glen Flora 

Spring 


St. Croix, 

Wis. 
Mineral 
Spring a 


Wauke- 
sha, Wis. 
Hygeia 
Spring 


Owatonna, 
Minn. 
Vichy 
Spring 










.69 


.28 


Sodium Sulphate. 


1.75 


1.85 


.52 


.45 








.71 
.46 


.18 
0.45 


.05 
.79 


'1.89 


.34 




52.41 




4.04 

4.63 

.21 

19.23 




Magnesium Bicarbonate . . 




11.09 


7.25 


8.40 




2.50 




Calcium Bicarbonate 


15.57 


11.19 


16.37 


Calcium Carbonate 


9.57 




Calcium Sulphate 






1.62 

.01 

| 3.04 

.71 
1.43 




Ferrous Bicarbonate 








.54 


Ferrous Carbonate 


.50 

} •» 


.11 
.15 
.91 


j .49 

.27 
1.43 




Alumina Carbonate 

Silica 


.10 
1 . 70 


Free Carbon Dioxide 


4.34 










Total grains per Gallon 


15.76 


36.31 


20.56 


37.50 


85.02 



a Spring from Potsdam Strata. 

sodium chloride and occasionally with many other salts. The waters 
from limestone regions commonly contain carbonates of lime and mag- 
nesia with various other salts. On account of the mineral content of 
ground waters, the consequent flow of streams is much harder during 
low water periods than during high water when the flow is derived 
largely from surface runoff. 

In the desert regions of the West the soils contain greater proportions 
of the alkaline salts which are detrimental to vegetation. Waters from 
such strata, when they rise to the surface or when they stand on the sur- 
face and evaporate, leave behind an alkaline residue which prevents the 
growth of vegetation and spoils the land for agricultural purposes until 



Qualities of Ground Water. 



415 



it is properly drained and the deposited salts are dissolved and carried 
away by the proper application of irrigation waters. 

Waters from underground sources which in general are more highly 
mineralized than surface waters are as a rule free from the grosser 
forms of pollution often found in surface streams. The soil and mantle 



TABLE 44. 

Mineral Character of Waters from Sandstones at Various Places in the Upper 
Mississippi Valley, Grams per U. 8. Gallon. 



Compound 


Jersey- 

ville, 111. 

Water 

Works 

Well 


Mon- 
mouth , 

111. 
Water 
Works 

Well 


Dekalb, 

111. 

Water 

Works 

AVell 


Rock- 
ford, 111. 
Water 
Works 
AVell 


Mad- 
ison, 
AVis. 
AVater 
AVorks 
AVell 


Sheboy- 
gan, 
AVis. 

Public 
AVell 


Potassiun Sulphate 

Sodium Sulphate 

Potassium Chloride 


10.. SO 

5.05 


4.86 
23.45 


[ 1.13 

} - 


.50 
.36 


.24 
.2!) 


14.48 


Sodium Chloride 

Magnesium Bicarbonate .... 
Magnesium Chloride 


85.93 
Trace 
15.53 


9.61 


.27 

Trace 

12.80 


.29 

Trace 

12.89 


306.04 


14.07 


6.47 


. 17 

54.01 


Calcium Chloride 












27 . 82 


Calcium Bicai'bonate 

Calcium Sulphate 

Ferrous Bicarbonate 

Alumina 


6.84 

16.91 

.11 

.06 

.78 


15.82 

4.70 

.24 

.10 

1.04 


8.39 


13.17 


15.24 


i :-; . m 

160.^3 


|- . 69 

.70a 
17.40 


.08 
.14 

.58 

.82 

28.72 


.21 
Trace 

1 .OH 

30.25 


.50 
13 


Silica 


.47 


Sodium Bicarbonate 


.33b 










Totals 


141.51 


73.89 


5S0 -'4 







* Organic. 

b Composed of chlorides of lithium, bromide of sodium and phosphates of 
line, with trace of soda, sulphate of baryta and bicarborate of soda. 

deposits undoubtedly have a purifying effect on polluted waters both by 
straining action and by the activity of nitrifying organisms in the upper 
soil. Nevertheless, the waters of many shallow wells are frequently 
grossly polluted by seepage from nearby vaults, cesspools and barnyards 
(Fig. 247) , and often deep wells are polluted in the same manner by im- 
proper casing through the mantle deposits. Springs and deep wells are 
also sometimes polluted by the passage of organic matter through open 
and cavernous formations (Fig. 248). Such pollution is of a most dan- 
gerous character because its existence is unseen and unrealized, and the 
clear and sparkling waters seldom give apparent evidence of their 
dangerous condition. 



416 



Ground Waters. 



191. Velocities and Quantities of Ground Water Flow. — In many 
places where ancient river valleys are filled with great deposits of sand 
and gravel there are extensive ground waters from which large supplies 
are sometimes obtained. (See Fig. 243.) The general public and 




Fig. 247. — Pollution of Wells from Surface Drainage of Streets and Seepage 
from Vaults (see page 415). 

sometimes engineers, in making estimates of the quantities that can 
be obtained from such sources, are misled by the large volume of water 
present in these deposits. The movement of such ground waters under 
their normal gradient is very low (see Table 45), and to secure a large 




Fig. 248. — Pollution of Spring from Surface and Subsurface Drainage ( see 

page 415). 

quantity of water from wells, filters, galleries, etc., a considerable de- 
pression must be created in the ground water plain in order to produce 
the comparatively large head necessary to increase the velocity and in- 
duce the desired flow. 

In the spring of 1918 such a source was proposed as a water supply 
for a large irrigation project in a Western state. During the spring" 
and fall water is available from a stream which, however, becomes drv 



Flow of Ground Water. 



417 



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Hydrology — 27 



418 



Ground Waters. 



for about six months during the principal irrigation season, and during 
this time water to the amount of 750 cubic feet per second would have 
to be obtained, if at all, from the ground water which in the upper val- 
ley is contained in coarse sand and gravels several miles in width and 
several hundred feet in depth, and from which large supplies are ob- 
tained from wells. The underflow at the outlet of the valley passes 
through the section shown in Fig. 249, with an area above the rock bed 
and below the stream bed of 50,000 square feet. Five thousand square 
feet of this is fine sand and silt, and 45,000 square feet is coarse sand 




Fiu. 249. — Underflow Section of a Western River. 

and gravel. The ground water above this section has a slope toward the 
outlet of nine feet per mile. The project involved an expenditure of 
about $2,000,000 and promised a large profit if the ground water supply 
was dependable. The engineer of the project reported that a sufficient 
supply could be obtained from this source. Was he correct? An in- 
vestigation of the probable flow in this cross section as shown, and on 
the assumption of the section being entirely filled with sands and gravels 
of various degrees of coarseness and with other ground water slopes, 
will furnish a point to the following discussion and show how important 
the subject of ground water flow may become under certain conditions. 
In investigating the flow of water through sand, experiments have 
been made on materials which could be examined, weighed, measured, 
and the porosity of which could be determined by various methods 
which the experimenter applied. Even under such conditions it has 
been found that the accurate determination of porosity and the effective 



Flow of Ground Water. 419 

size of the material are attained only by careful manipulation, and that 
where crude methods are applied to such measurements very discordant 
results are obtained. 

In the formulas derived from the experiments of Hazen 11 and 
Slichter, 1 - an "effective size" of sand or soil grains, expressed in milli- 
meters, is used to define the comparative coarseness of the material ; but 
each experimenter determined this by a different method, and there 
is no known basis of comparison between them. These form- 
ulas are inapplicable unless "effective size" of the material and other 
factors are determined in the same manner and with the same degree 
of care and skill as in the case of the original experiments, and even 
then they will apply only to conditions of uniformity and kind of ma- 
terial used in the original experiments and which can be found only 
under experimental conditions. 13 

The general principles that underlie the flow of ground water through 
porous soils are as follows : The velocity of flow will 

i. Increase directly with the head or difference in elevations between 
the water at the inlet and outlet of the column of soil. 

2. Decrease directly with the length of travel through the column of 
soil considered. 

3. Increase rapidly with the size of the pores of the water bearing 
material. 

4. Increase rapidly with the porosity or percentage of voids in the 
water bearing material. 

5. Increase with the temperature of the flowing water. 

Darcy, 14 who made the first attempt to investigate this subject, pointed 



11 Annual Report Mass. State Board of Health, 1892, p. 541. Some Physical 
Properties of Sands and Gravels with Special Reference to Their Use in Fil- 
tration, Allen Hazen. 

Note — Mr. Hazen has called attention to the purpose of these investigations 
and cautioned against the use of his formula under conditions foreign to those 
from which it was derived. See A. S. C. E., Vol. 73, p. 199. 

v Nineteenth Annual Report U. S. Geological Survey, 1897-98, Pt. 2, C. S. 
Slichter, Theoretical Investigations of the Motion of Ground Water; also 
Water Supply Paper No. 67, C. S. Slichter, The Motion of Underground Water. 

is When the problem of the engineer is such that the size of grains and 
character of the material can be determined (as in flow through filter sands) 
he should refer to the original discussion of this subject as a basis for his 
calculations for information concerning methods of determining porosity and 
effective size. 

"Les fontanies publiques de la ville de Dijoin H. Darcy, 1856, Paris. 



420 Ground Waters. 

out that the velocity of flow through soil is directly proportional to the 
head and inversely proportional to the length of flow ; that is 

h 

(1) v = k — 

1 
Where 

v = Velocity of flow (in feet per minute) 
h = Head acting on the soil section (in feet) 
1 = Length of the column or soil section (in feet) 
- k = A factor of flow to be determined experimentally for each ma- 
terial 

Slichter's formula for estimating the flow of water through a column 
of sand is as follows : 

hd a 

(2) q = 0.2012 

fdK 
in which 

q = Quantity of water transmitted by the column per minute 

h = The head producing the flow (in feet) 

a = Area of the cross section of the sand bed ( in square feet ) 
1 = Length of travel of the water 

d = The effective diameter or effective size of the sand grains 

n = A viscosity coefficient (which decreases rapidly with an in- 
crease in temperature) 

K = Porosity coefficient (varying with porosities of from 20 to 47 
per cent) 

The part of the expression varying with the character of the soil may 
be represented by a coefficient or transmission constant, k, when Equa- 
tion 2 becomes 

ha 

(3) q = k — 

1 

which is essentially the same as the formula of Darcy. 

As has previously been noted, the formulas of. the type of Equation 2 
for the flow of water through sand, etc., are all dependent upon the ac- 
curate determination of porosity and effective size of the porous medium. 
This effective size is dependent on the nature of about ten per cent, of 
the finest material, and there is no method uniformly applicable by which 
this effective size can be accurately determined for all classes of material. 
Even the porosity of a fine material cannot be determined without great 
care, for this factor depends not only on the size and shape of the grains 
but on the method of packing as well, and a removal of samples from a 
natural bed will alter their arrangement and may affect the porosity. 

In estimating the flow of ground waters both the porosity of the ma- 
terial and the effective size of the grains must be assumed, or at best, de- 
termined only at a few points, while the porous beds may extend for 



Flow of Ground Water. 421 

miles and actually vary in both factors every few feet throughout their 
entire extent. The answer to the problem must therefore be found by 
estimating" what probably would occur if the porous medium had a cer- 
tain porosity and a certain definite character, and on this basis calculat- 
ing limiting values which will afford a much better guide to the engineer 
than an assumption of flow based on the desire of the investigator to 
secure a certain quantity of water for a certain purpose. 

It should be understood that any calculations of the velocity of flow 
of ground water can be regarded only as a rough approximation which 
will undoubtedly vary widely from the truth as developed by actual de- 
termination of flow by experiment or from the measurement of flow 
into wells, infiltration galleries, etc., and in consequence large factors of 
safety must be allowed in making estimates which are to serve as bases 
for investments. 

From Equation 3 it will be seen that the flow of water through fine 
materials where capillary attraction is effective is found to vary directly 
with the slope ; then the flow for a slope of io c /o is one-tenth of the 
amount of flow under unity slope (see Table 48) , while for slopes of 1 % 

it is .01, for .\ c /c it is .001, and for a slope of a foot per mile orr- 
it is .00189 of the flow for unity slope. This does not apply to coarse 
gravels when the velocity of flow varies more nearly with \/h. 

Slichter has found that the flow of water will increase rapidly with 
the temperature, and that the flow at various temperatures compared 
with the flow at the temperature of 50 F., taken at unity, will vary as 
shown in Table 46. He also finds that the flow of water rapidly in- 

TABLE 4G. 

Effect of Tevi per ■xture on Flow of Water Compared toith Floiv at 
50° F. = 1.00 
Temperature 

Fahrenheit 32" 35" 40" 50°' 55" G0° 65" 70° 75° 80° 90° 
Relative 
Flow .74 .78 .85 1.00 1.0S 1.16 1.25 1.34 1.42 1.51 1.70 

creases with the porosity, and that the flow for various porosities com- 
pared with the flow for a porosity of 32^ taken as unity will vary as 
shown in Table 47. 

TABLE 47. 

Effect of Varying Percentages of Porosity on Flow of Water Compared ivith 

Porosity at .12% = 1.00 
Porosity or 
Percent of Voids 30 32 34 36 38 40 

Relative Flow .81 1.00 1.22 1.47 1.76 2.09 



422 Ground Waters. 

Slichter has also determined that the flow of water through various 

classes of material will vary under conditions of 50 F. temperatures, 

32% porosity and with unity gradient, approximately as given in 

Table 48. 

TABLE 48. 

Transmission coefficient (k) or Velocity of Flow of Water with Unity Slope at 
■50° F. and 32% Porosity in Various Soils. 





Silt 
.00012 
.002 


(In feet per 


minute) !3 

Sand 




Fine 


From 

To 


Very Pine 
.003 
.009 


P"ine Medium 
.011 .07 
.046 .26 


Coarse 

.28 
1.02 


Gravel 
1.1 

28.0 



The quantity of water flowing in a given section of material may be 
found by the expression 
( 4 ) Q = vap 

in which 

Q = Cubic feet per minute 

v = Velocity determined as above 

porosity 

a = Area of cross section x 

100 
p = Porosity 

For example, determine the quantity of water flowing through 1000 
square feet of fine gravel (of maximum coarseness) with a temperature 
of 60 ° Fahr., a porosity of .40 and a gradient of 20 feet per mile. The 
flow at unity gradient in such material is 28 feet per minute, and a gradi- 
ent of f , ■ = .00379 I hence the velocity of flow at this gradient will be 

.00379 times 28 = .106 feet per minute. For a temperature of 60 ° F. 
this will be increased by 16%, and for a porosity of .40 by 109% ; hence 
the actual velocity will equal .106 times 1.16 times 2.09 = .257 feet per 
minute. The flow area a p will equal 1000 square feet times .40 = 400, 
and the quantity of flow will equal .257 times 400 = 103 cubic feet per 
minute or 1.7 cubic feet per second. 

The opportunities for gross errors in such computations as are made 
above are obvious, and yet the extreme case which can reasonably be 
assumed will often correct false impressions of possible capacities which 
otherwise would lead to serious results. Where more detailed informa- 
tion is necessary, it may sometimes be secured by the actual measure- 

ir ' The transmission coefficient k is the flow that will take place in a column 
of the selected material of standard porosity (32 per cent) at standard tem- 
perature (50° Fahr.) and under unity slope, that is with a head (h) equal to 
the length of the column of material (I) which condition is found in a vertical 
column with the water surface standing at the surface of th2 material. 



Flow of Ground Water. 423 

ments of ground water velocity as suggested by Slichter in 1902. 1G 
Prof. Slichter's method is to sink two or more wells into the underflow, 
separated in the direction of flow by a certain known distance. By in- 
troducing an electrolyte into the higher well and utilizing electrical 
means, the time of passage of the water containing the chemical can be 
ascertained by the deflection of an ammeter needle and the velocity of 
the underflow thus determined. It is to be noted that the velocity of 
the underflow in different parts of a section varies greatly in accordance 
with the materials, the porosities and the contour of the underground 
channel. (See Fig. 250.) 




Fig. 250. — Velocity of Ground Water at Various Points in the Section of the 
Narrows of the Mohave River. After Slichter. 

192. Wells. — Wells are excavations from the surface into underlying 
deposits and are usually constructed for the purpose of obtaining under- 
ground water for various purposes. In general, the waters have to be 
raised by some form of pump but occasionally with artesian conditions 
the water will flow at the surface. A well is therefore an artificial out- 
let for ground water, and when pumping is begun the first effect is to 
lower the hydraulic gradient or level of the ground water in the immedi- 
ate vicinity of the well sufficiently to create the head necessary to pro- 
duce the desired flow. 

Wells in cracked, fissured and cavernous rocks (Fig. 251) depend on 
local conditions for their yield. These conditions can seldom be de- 
termined except by actual construction, although previous local experi- 
ence may furnish a valuable guide as to what may be expected in new 
construction. Successful wells in crystalline and limestone rocks must 
reach water bearing cracks or fissures and a failure to encounter such 



10 Water Supply Paper No. 67, by C. S. Slichter, The Motion of Underground 
Water. Water Supply Paper No. 110, C. S. Slichter, Underflow Meter used in 
Measuring Movements of Underground Waters. 



424 



Ground Waters. 



conditions will result in dry wells (Fig. 251, A & B). Wells in clay 
deposits containing sand beds or pockets are subject to similar contin- 
gencies (Fig. 251, C). Sometimes adjacent wells may furnish supplies 
of water which differ widely in mineral content or in organic purity on 
account of quite different sources from which their supplies are de- 
rived. (Fig. 251, D.) 




>?. Dry and Wafer Searing Wef/s 
/n Crysfa///ne Rock 



8. Dry and Wafer 3ecrr/nc? We//s 
in L /m esfone. 




C. Ory and Wafer 3ear/ny kYe/fs /'n 
C/ay Contc/n/na Sand and Gnare/ Beds. 



D. ffard trnef Soff Wafer from 
Adjacent We//s. 



Fig. 251. — Conditions Favorable and Adverse to Securing Satisfactory Wells. 

The quantity of water which may be secured from any well can in 
general be determined only by actual test. Such tests are usually made 
by pumping the well continuously for a considerable period ; but even 
then the effects of long dry periods on the supply can only be estimated. 
For small supplies such tests are quite satisfactory but for large sup- 
plies the ultimate results are more or less problematic. 

The principles of the flows of water in beds of sand and gravel of 
fairly uniform character are more readily determined. The principles 
of flows into wells are essentially the same as those for natural flow of 
ground water into streams or other natural outlets, and the continuous 
operation of the well tends to exhaust the ground water, to reduce its 
elevation in adjacent strata and gradually to increase the depth from 
which it has to be raised. As the water producing area created by the 



Wells. 425 

construction of the well is comparatively small, the gradient necessary 
for the production of considerable supplies is correspondingly large. 

Turneaure 17 has shown that when a well is sunk through any water 
bearing sand stratum the flow will be given by Equation 5. 

(5) 




in which 

Q = Quantity of water in cubic feet per day 

r = The radius of the well in feet 

k = Transmission constant of material 

p = Porosity of the water bearing material 

h = Height of water above the base of the water bearing 

stratum 
y = Height of any point in the ground water plain above the 

bottom of the well at x distance from the well 
x = Distance of any point in the ground water plain from the 

center of the well 
loge x = Hyperbolic logarithm of x 

From this equation the slope of the cone of depression can be deter- 
mined. (Fig. 252, A.) 

When pumping first begins this area of depression will gradually 
widen and affect the ground water for some considerable distance in 
every direction, and its slope will be somewhat modified by the normal 
slope of the ground water and the direction of its flow. The continu- 
ous pumping of wells from superficial deposits will gradually reduce the 
ground water level at continually increasing distances from the well 
until, if the supply be sufficient, a new ground water gradient is es- 
tablished which will be maintained as long as the relations of supply and 
demand obtain. If the supply is practically inexhaustible, the cone of 
depression will finally assume a permanent form with a fixed circle of 
influence having a diameter x beyond which the ground water will not 
be lowered and the ordinate y will equal H. Under these conditions 
Equation 5 may be written 18 

Trkp ( H + h ) ( h — h ) 

(0) Q = 

x 

log, — 
r 

From which it is apparent that the supply will be proportional both to 
H -\- h and to H — h, which has been found to be the case in many 



it Public Water Supplies, F .E. Turneaure and H. L. Russell, 2d Ed., 190S, 
p. 279. 

is Ibid, p. 213. 



426 



Ground Waters. 



actual tests. From this equation it is understood that for small de- 
pressions in the ground water level the quantity of water will vary al- 
most directly with the head but that for considerable depressions the 
increase in quantity is small. (Fig. 252, B.) 

In deep wells where the reduction in head even if considerable is 
usually small with relation to the total depth of the wells, the flow is al- 
most directly proportional to the reduction in head below the hydraulic 
gradient. (Fig. 253.) 

When, however, the diameter of the well is small in proportion to the 



Ground Leyet 




v: 


fte/af/re r/e/ct 
0.2 0.4 0.6 0.8 


/.C 


\> 






















kaa 










































.r 

Y 6 


















































































\ 






















■£• 0.8 

X 






















> 

<* 























/Q. Cone of Depression of Ground 
Water 



B. jRe/ot/on of Reduction of fteacf 
to r/e/ct of We//s 



Fig. 252. — Principles of the Hydraulics of Wells. 



flow, the friction in the casing will reduce the discharge and this effect 
must be taken into account in any estimate of the yield of wells. 10 

The elevation of ground water in wells is subject to all the seasonal 
variations of supply together with the additional factor of demand 
created by its use. The waters rise and fall with the rainfall and the 
season (Fig. 254), and the depth of the well and the pumping appliances 
used must be adjusted to meet all such conditions. As noted, every 
well in active operation creates in the surrounding water bearing strata 
a cone of draft dependent upon the principles discussed and affects the 
ground water gradient for a greater or less distance from the well, in 
accordance with the demand for water and the pervious character of 
the strata. 

Where a single well is insufficient to supply the amount of water de- 
sired, and additional wells are constructed, they must for economical 



10 See Public Water Supplies, F. E. Turneaure, page 287. 



Wells 



427 




20 40 60 80 /OO /BO /40 /60 /SO 200 220 240 260 280 300 
r~/ow in 7~housarnds of Ga//ons per Day 

/3. f^/orv of We//s af ancf aSove Grounaf Leve/ 

Surface of Ground-^ 



eo 

40 

60 

80 

/OO 

/eo 

/■40 
/60 
/80 

200 

220 
240 

































































57a-/ 


C fl 


'ecrd 


A 


>o r 


/or*f 


1 






























jl 






















































K^-t 


~xpe 


'-/me 


*r?fa 


/ /= 


'o/hf 


s. 




















































>sP 













































































































































1 8/2/6 20 24 28 82 36 40 44 48 S2 S6 60 
f^/orv in 7~r>OLisands of Ga/ions per ^ o y 

S. r~/or* of We/is 6e/or* Ground Level ( Determined by flumping-) 
Fig. 253. — Flow Measurements from Certain Australian Wells.* 



♦Artesian System of Western Queensland, C. J. R. Williams, Proc. Inst. C. E , 
Vol. 159, p. 315, 1904-5. 



428 



Ground Waters. 



/9/3 Z9/-4 /9/S /9/6 

s oNDjrrJA/*?ji/A 5 o/vDurnAnjjA 5 o /v dj rnArr 




Fig. 254. — Variations in the Elevation of Water Surface in Wells due to Rain- 
fall and Season. After Meinzer (see page 426). 



Grour-rc/ Lere/ 




Fig. 255. — Illustration of the Interference of Wells. 

reasons be constructed at sufficient distances from other wells so as not 
to interfere greatly with the cone of draft ; otherwise the capacity of the 
wells so constructed will be reduced (Fig. 255). It is usually impracti- 
cable to construct wells in such manner that no interference will occur 
and various practical considerations must furnish a basis for their 



Wells. 429 

proper adjustment. Where flowing wells are developed in the artesian 
areas they often furnish a convenient and economical method of obtain- 
ing water supplies, especially when the flow is sufficient to meet the de- 
mand. A successful well of this kind in a thickly populated commun- 
itv, however, soon brings about the construction of similar wells and as 
the wells increase in number and the quantity of water obtained increases 
in volume, the hydraulic gradient is gradually reduced until the supply 
required is so great that the wells cease to flow and pumping appliances 
have to be introduced in order to obtain the necessary supplies. As the 
demand for water supply increases the hydraulic gradient is farther and 
farther reduced until finally the water has to be raised from a consid- 
erable depth and the necessary expense involved finally limits the de- 
mand. The hydraulic gradient then becomes essentially permanent if 
the quantity of water in the strata and the drainage area of its outcrop 
are sufficient to maintain it. 

LITERATURE 

GROUND WATER 

Some Physical Properties of Sands and Gravels, with Special Reference to 

Their Uses in Filtration, Allen Hazen, Annual Report State Board of 

Health, 1892. See also Trans. Am. Soc. C. E., Vol. 73, p. 199, 1911. 
Principles and Conditions of the Movements of Ground Waters, F. H. King, 

19th Annual Report U. S. G. S., Pt. 2, 1897-8, p. 67. 
Theoretical Investigation of the Motion of Ground Water, C. S. Slichter, 19th 
•Annual Report U. S. G. S., Pt. 2, 1897-8, p. 295. See also Water Supply 

Paper No. 67, 1902. ' 
The Rate of Movement of Underground Water, C. S. Slichter, U. S. G. S. Water 

Supply Paper No. 140, 1905. 
Underground Water Resources of Long Island, N. Y., A. C. Veatch, C. S. Slichter 

and others, U. S. G. S. Professional Paper No. 44, 1906. 
The Underflow of the South Platte Valley, C. S. Slichter and H. G. Wolff, U. S. 

G. S. Water Supply Paper No. 184, 1906. 
The Underflow in Arkansas Valley in Western Kansas, C. S. Slichter, W. S. & 

Irrigation Paper No. 153, 1906. 
Underflow Tests in the Drainage Basin of Los Angeles River, Homer Hamlin, 

U. S. G. S. Water Supply Paper No. 112, 1905. 
Bibilographic Reviexo and Index of Papers Relating to Underground Waters 

published by the U. S. Geological Survey from JS79 to 190 h, M. L. Fuller, 

U. S. G. S. Water Supply Paper No. 120, 1905. 
Bibliographic Reviexo and Index of Underground Water Literature in 1905, 

Fuller, Clapp and Johnson, U. S. G. S. Water Supply Paper No. 163, 1906. 
Experiences had During the Last Twenty-five Years with Water Works having 

Underground Source of Sujoply, B. Salbach, Trans. Am. Soc. C. E., Vol. 30, 

p. 293, 1893. 
Water Resources of Illixwis, Frank Leverett, 17th Annual Report U. S. G. S., 

1896-7, Pt. 4, p. 480. 



430 Ground Waters. 

Preliminary Report on the Geology and Water Resources of Nebraska West of 
the One Hundred and Third Meridian, N. H. Darton, 19th Annual Report 
U..S. G. S., 1897-8, Pt. 4, p. 719. 

Geology and Underground Water Resources of the Central Great Plains, N. H. 
Darton, U. S. G. S. Professional Paper No. 32, 1905. 

Underground Water Investigations in United States, M. L. Fuller, Economic 
Geology and American Geologist, Vol. I, No. 6, June, 1906. This paper 
contains a number of references on the subject of ground water. 

The Underground Water Resources of Alabama, E. A. Smith, Geological Sur- 
vey of Alabama, Univ. of Alabama, 1907. 

A Preliminary Report on the Underground Water Supply of Central Florida, 
E. H. Sellards, Bulletin No. 1, Florida State Geological Survey, 1908. 

Public Water Supplies, Turneaure and Russell, Wiley and Sons, Pub., Chap. 7, 
p. 87, 1908. 

Underground Waters in Crystalline Rocks, F. G. Clapp, Eng. Rec. Vol. 60, 
p. 525, 1909. 

Underground Waters in Slate and Shale, F. G. Clapp, Eng. Rec, Vol. 59, p. 751, 
1909. 

Groundwater Supply and Irrigation in the Rillito Valley, G. E. P. Smith, Bul- 
tin No. 64, Agr. Exp. Sta., Univ. of Arizona, 1910. 

Geology of Soils and Szibst7-ata, H. B. Woodward, Edw. Arnold, London, 1912. 

The Undergrounds Water Supply of West Central and West Florida, E. H. Sel- 
lards and Herman Gunter, 4th Annual Report Florida Geol. Survey, 1912, 
p. 81. 

Ground Waters as Sources of Public Water Supplies. Wm. S. Johnson, Jour. 
N. E. W. W. Asso., Dec. 1909. 

The Underground Waters of North Central Indiana, Stephen R. Capps, Water 
Supply Paper No. 254, U. S. G. S.. 1910. 

Underground Waters for Farm Use, Myron L. Fuller, Water Supply Paper 
No. 255, U. S. G. S., 1910. 

Wells as Sources of Supplementary Water Supplies, Myron L. Fuller, Eng. 
News, Sept. 12, 1912. 

Ground Water Supplies, Wm. S. Johnson, Jour. Boston Soc. C. E., May, 1915. 

Water Supplies of Wisconsin, S. Weidman and A. R. Schultz, Bui. No. 35, Wis. 
Geol. & Nat. Hist. Survey, 1915. 

Watei-works Handbook, Flinn, Weston and Bogert, Chap. 4, p. 73, McGraw- 
Hill Book Co., N. Y., 1916. 

Water Supply, William P. Mason, Chap. VIII, p. 373, Wiley and Sons, 1916. 

Qualitative Estimation of Ground Waters for Public Supplies, Myron L. Fuller, 
Jour. N. E. W. W. Assoc, June, 1913. 

Geology and Water Resources of Big Smoky, Clayton and Alkali Spring Val- 
leys, Nevada, O. E. Meinzer, U. S. G. S. Water Supply Paper No. 423, 1917. 

For references concerning seepage and percolation see literature for Chap- 
ter VI. 

ARTESIAX AND DEEP WELL WATERS 

Requisite and Qualifying Conditions of Artesian Wells. T. C. Chamberlain, 5th 

Annual Report U. S. G. S., 1884, p. 131. 
Flow of Artesian Wells and Their Mutual Interference, C. S. Slichter, 19th 

Annual Report U. S. G. S., p. 358, 1897-8. 



Literature. 43 1 

Artesian Flows from Unconfined Sandy Strata, Myron L. Fuller, Eng. News, 

Mar. 30, 1905, p. 329. 
The Interference of Wells, Frederick G. Clapp, Eng. News, Vol. 62, p. 483, 1909. 
Basic Principles of Ground Water Collection, Charles B. Burdick, Am. W. W. 

Asso., June, 1913. 
Drilled Wells of the Triassic Area of the Connecticut Valley, W. H. C. Pynchon, 

W. S. & Irrig. Paper No. 110, p. 95, 1904. 
Spring System of the Decaturville Dome, Camden County, Missouri, E. M. 

Shepard, W. S. & Irrig. Paper No. 110, p. 113, 1904. 
Deep Borings in the United States, N. H. Darton, W. S. & Irrig. Paper No. 57, 

1902, No. 61, 1902, and No. 149, 1905. 
Record of Deep Well Drilling for 190'/, M. L. Fuller, E. F. Lines and A. C. 

Veatch, U. S. G. S. Bui No. 264, 1905. 
Record of Deep Well Drilling for 1905, M. L. Fuller and S. Sanford, U. S. G. S. 

Bui. No. 268, 1906. 
Flowing Wells and Municipal Water Supplies in the Southern Portion of the 

Southern Peninsula of Michigan, Frank Leverett, W. S. and Irrig. Paper 

No. 182, 1906. 
The Underground Water Resources of Alabama. Eugene A. Smith, State Geolg- 

ist, Geol. Survey of Alabama, 1907. 
Geology and Underground Waters of Luna Co., Neiu Mexico, N. H. Darton, U. 

S. G. S. Bui. No. 618, 1916. 
Preliminary Report on Geology and Water Resource of Nebraska West of the 

One Hundred and Third Meridian, N. H. Darton, U. S. G. S. Professional 

Paper No. 17, 1903. 
Artesian Wells of Ioiva, W. H. Norton, Iowa Eng. Soc. 1898. 
Artesian Well Practice in Western United States, Compiled from Government 

Report, Eng. News, Vol. 25, p. 172, 1891. 
Artesian Wells of Colorado, Colo. State Agric. College Bulletin No. 16, 1891. 
Artesian Wells in Kansas, Robert Hay, 22d Report Kansas Academy of Science. 
Notes on Artesian Water and the Effects of D'rigation on Sub-Surface Water in 

the San Joaquin Valley, Eng. Record, Vol. 31, 1894. 
Artesian Wells in the Red River Valley, Warren Upham, Monograph No. 25, 

U. S. G. S. The Glacial Lake Agassiz, p. 550. 
The Geological Structure of the Extra- Australian Artesian Basins, Maitland, 

Proc. Royal Soc. of Queensland, Vol. XII, April 17, 1896, Relates to the 

Artesian Basins of the United States. 
Wells of Northern Indiana, Frank Leverett, U. S. G. S. Water Supply Paper 

No. 21, 1899. 
Wells -of Southern Indiana, Frank Leverett, U. S. G. S. Water Supply Paper 

No. 26, 1899. 
The Ground Wate7S of a Portion of South Dakota, J. E. Todd, U. S. G. S. Water 

Supply Paper No. 34, 1900. 
The Artesian System of Western Queensland, C. J. R. Williams, Proc. Inst. 

C. E., Vol. 159, 1904-5, p. 315. 



CHAPTER XVI 

STREAM PLOW OR RUNOFF 

193. Source of Runoff. — The water flowing in streams is derived 
from two sources, the amount of each being dependent upon the rain- 
fall and on many other physical conditions on the drainage area : 

1. That portion of. the rainfall which passes directly, into the streams 
as surface flow and which is the principal cause of sudden increase in 
flow and of floods. 

2. That portion of the rainfall which sinks into the ground to reappear 
as springs and ground flow at more or less distant points, and which in 
general is the principal source of the ordinary dry weather flow of 
streams, although in some cases surface storage (i. e. lakes and swamps) 
becomes a still more important source of dry weather flow. A portion 
of this seepage may pass into the deep strata and flow away from the 
drainage area, reappearing in the lower valley or perhaps in distant 
areas, or even in the sea, but such losses from the seepage water are 
usually very small. 

The runoff is that portion of the rainfall that is not absorbed by the 
deep strata, utilized by vegetation or lost by evaporation and which finds 
its way into streams as surface flow. The demands of seepage, vegeta- 
tion and evaporation are usually first supplied and the runoff is therefore 
the overflow or excess not needed to supply these demands on the rain- 
fall, or that portion which, on account of topographical conditions, has 
moved so rapidly that seepage and evaporation have not had time to 
affect it. 

The portion of the flow of streams derived from the ground water is 
that portion of the seepage on the drainage area that has passed down- 
ward into cracks, fissures or porous beds of the higher parts of the drain- 
age area, until it has encountered impervious material which has pre- 
vented its further descent and forced it to some outcrop that has been 
exposed by the development of the drainage channel into which it dis- 
charges. 

194. Importance of the Study of Runoff. — The study of runoff is 
important to the engineer in connection with the investigation of public 
water supplies, water power, irrigation, drainage, storm water sewerage. 



Study of Runoff. 433 

flood protection, navigation, river regulation, etc. In general, the in- 
terest of the engineer centers around three phases of this question : 

i st. The total quantity of flow, its annual and seasonal variation and 
the possible methods of its equalization or concentration. 

2d. The maximum quantity of flood flow, its variation during the 
period of flood, and its reduction or control. 

3d. The minimum flow and its possible modification by storage or 
auxiliary supply. 

Averages are of little moment. It is not satisfactory to show that the 
average water supply is sufficient if in one season or year there are flood 
conditions and in another there is a serious shortage of water or per- 
haps no water at all available. Water like food must be available when 
needed, and averages are almost valueless for most engineering pur- 
poses. A public water supply must command an adequate quantity 
essentially constant during the year and increasing with the growth of 
the community. A supply for irrigation must be adequate in quantity 
and available during each growing season. For successful water power 
development a continuous adequate supply must be existent or must be 
made available or else auxiliary power must be provided to take its 
place. For navigation a sufficient supply must be available during 
every navigation season. 

In flood protection, drainage, storm water sewerage, and in the design 
of spillways, channels or reservoirs to pass or control the high waters of 
flood periods, the question of the maximum flow and the rate of increase 
and subsidence of floods are matters of the greatest importance. 

In some engineering problems the whole range of variation is of im- 
portance, while in others the maximum or minimum may be the import- 
ant factor. 

195. Occurrence of Runoff. — In general upland areas are wet only 
during and for a short time following rainstorms until the moisture 
sinks into the soil or rock, is taken tip by vegetation or is evaporated, or 
until the surface water drains into the lower lands. 

The lower lands remain wet for a longer period as they receive not 
only the direct rainfall but also the surface runoff and perhaps the seep- 
age from the saturated soils of the higher lands. When drainage is 
poor the low lands may hold the water for considerable periods and in 
the case of swamps and marshes may be permanently overflowed ex- 
cept possibly in very dry seasons, while in other cases, permanent pools, 
swamps and lakes that are never known to become dry result from im- 
perfect drainage. 

Hydrology — 28 



434 



Stream Flow or Runoff. 



The channels of streams undergo similar variations. Even in humid 
regions with small drainage areas and high gradients drainage channels 
may rapidly pass the waters from a rainstorm and in a few days or even 
hours become as dry as the surrounding country. In such cases these 
drainage channels are called dry runs. In streams draining larger areas 
in humid countries, the varying rainfalls and consequent runoff from 
widely separated areas, the seepage from porous soils and the drainage 




Fig. '2r>G. — The Colorado River at Austin, Texas, in Flood. 

of lakes and swamps furnish a constant supply, variable in magnitude 
but perhaps seldom or never failing and stream flow becomes perennial. 

In arid and semi-arid countries the variation in flow is more marked 
and the drainage channels from greater areas become dry at times. The 
Colorado River at Austin, Texas, drains an area of about 37,000 square 
miles and the runoff has been known to vary in quantity from 250,000 
cubic feet per second to 9 cubic feet per second. This wide range in flow 
of the Colorado River is well illustrated by Fig. 256 which shows the 
river passing over the dam during flood stage, and Fig. 257, which shows 
the extreme low water flow passing through a narrow channel and 
through a single gate in the dam. 

The wide variation in the flow of streams is also shown by Figs. 258 
to 261, pages 436 to 439 inclusive. In each case the variation in the 
flows of the twenty streams used as examples is illustrated by an annual 



Occurrence of Runoff. 



435 



hydrograph for a year of high flow and a year of low flow, so that 
approximately maximum and minimum conditions are indicated. These 
rivers are so chosen as fairly to represent the great variations in flow 
in different parts of the United States ; and the location of each stream 
is shown by the map, Fig. 262, page 440. These hydrographs show that 
the variations from day to day are. great and that while in general the 




Fig. 257. — Extreme Low Water Flow of the Colorado River at Austin, Texas.* 

high water and low water seasons in any stream are essentially similar, 
they nevertheless are subject to considerable variation. It is quite evi- 
dent from these hydrographs that the subject of runoff is by no means 
a simple one and that for practical engineering purposes even approx- 
imately correct conclusions call for a careful consideration of the many 
factors on which depend the great variations in flow of different streams 
and even of the same stream. 

196. Difficulties of the Problem. — Practical problems in stream con- 
servancy involving questions of water supply are greatly complicated 
by the numerous factors which modify or control this phenomenon and 
which are so intimatelv related and intermixed in their effects that the 



*Photo by Mr. Guy Collett, Austin, Texas. 



436 Stream Flow or Runoff. 

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Fig. 258. — Hydrographs of Various Streams for Years of High and Low Flow. 



Hydrographs. 



437 



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Fig. 259. — Hydrographs of Various Streams for Years of High and Low Flow. 



438 



Stream Flow or Runoff. 



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Fig. 260. — Hydrographs of Various Streams for Years of High and Low Flow. 



Hydrographs. 



439 



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440 



Stream Flow or Runoff. 




Factors of Runoff. 441 

relative influence of individual factors, if independently considered, be- 
comes difficult to differentiate and practically impossible to evaluate. 
The effects of individual factors considered under such a multiplicity of 
varying influences are therefore frequently misunderstood and often 
misinterpreted. If, however, the factors of fundamental problems are 
first considered in their most simplified relation and their effects under 
such conditions determined, the modifying effects of additional com- 
plicating factors can then be more readily understood and appreciated. 

For engineering purposes, the conditions of uniformity of flow and 
sufficiency of water supply are the most favorable and the conditions of 
maximum variation in flow and deficient water supply are the most un- 
favorable. From personal observation of the flows of numerous streams 
in which certain factors largely predominate, it is not difficult to differ- 
entiate the effects and segregate those conditions which will, if prevail- 
ing, result in either the most favorable or the least favorable water sup- 
ply of the consequent streams. Such conditions are outlined in Cases 
I, II and III, in Sections 205 to 208. 

197. The Factors of Runoff. — The factors which control or modify 
the runoff of streams are so inter-related that when any enumeration 
of such factors is made the question may logically be raised as to whether 
some of those listed are not similar to or a part of others, and almost 
any such enumeration might be classified and discussed in other ways 
with equal reason. 

For the purpose of this discussion these factors are listed as follows : 

i. Precipitation. 

2. Geographical relations of the drainage area. 

3. Topography and Geology. 

4. Meteorological conditions. 

5. Surface conditions. 

6. Storage conditions. 

7. Artificial use and control. 

A detailed consideration of these factors of stream flow, both individ- 
ually and in their inter-relations, -is necessary for the intelligent study 
and understanding of stream flow. Such a consideration within the 
limits of a single volume is impossible. The principal factors and their 
brief consideration are summarized in the following sections. 

198. Precipitation. — Precipitation is of primary importance for with- 
out precipitation there can be no stream flow. Precipitation modifies 
runoff in accordance with the quantity and manner of its occurrence. 



442 Stream Flow or Runoff. 

The important factors of precipitation to be kept in mind in the study 
of runoff are as follows : 

A. Causes of Precipitation. (See Sec. 82, p. 159.) 

a. Local conditions which may give rise to precipitation. (See 

Sec. 84, p. 165 et seq.) 

b. Movements of storms which produce precipitation. (See 

Sec. 40, p. 66.) 

B. Factors of Local Precipitation. (See Sees. 84 to 88, p. 165.) 

a. Location relative to sources of vapor from which precipitation 

is derived. (See Sec. 85, p. 166.) 

b. Location relative to storm tracks. (See Sec. 92, p. 176.) 

c. Local topography. (See Sec. 84, p. 165, also Chap. XII, 

p. 283 et seq.) 

C. Quantity and Distribution. (Chaps. IX and XL) 

a. Total annual amount of precipitation and its variations. 

(Chap. IX, p. 200.) 

b. Distribution of precipitation throughout the year, and varia- 

tions. (Chap. X, p. 228.) 

c. Intensity of individual storms. (See Sec. 119, p. 243, et seq.) 

d. Geographical extent of storms. (See Sec. 129, p. 266, et seq.) 

D. The Amount which occurs as Snow : 

The quantity that falls as snow or which freezes as it falls is re- 
tained (less evaporation) on the drainage area until higher 
temperatures cause it to melt and to flow to the stream, 
perhaps some weeks or months later. • 
In general, the following conclusions are warranted . 
Other things being equal, runoff will increase : 

With the total amount of rainfall (with exceptions). 
As the intensity of the rainfall increases. 
As the extent of the storm on the drainage area increases. 
As and when evaporation decreases (in fall, winter and spring). 
When vegetation is inactive (in fall, winter and spring). 
With precipitation stored as snow and ice (in spring). 
With precipitation stored underground (dry weather flow). 
Precipitation will have comparatively little effect on runoff : 

When it occurs in very light showers. 

When evaporation and vegetation are active (in summer). 

When the storm covers only a small portion of the drainage area. 



Precipitation. 



443 



Fig. 263 shows the relations of the total annual rainfall to the total 
annual runoff on four American streams, viz., the Sudbury, the Ohio, 
the Merrimac and the Coosa. 



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Fig. 263. — Relation of Total Annual Rainfall to Total Annual Runoff on Cer- 
tain Streams in the United States. 



It will be noted that while in general the runoff increases with the in- 
crease in rainfall there are exceptions to the rule and that evidently no 
constant relations exist. 



444 Stream Flow or Runoff. 

199. Geographical Relation of Drainage Area. — The important 
factors in these relations are (a) size, (b) shape, and (c) location of 
the drainage area. Each of these factors may have a marked effect on 
the quantity and regularity of the flow of a stream. 

(a) Most storms are more or less limited in extent but often include 
centers of high concentration. A limited storm might cover a relatively 
small drainage area with marked effect on the runoff, but would have a 
much different comparative effect on the flow from a large area. 

A small area which becomes the center of intense precipitation will 
furnish relatively great flood discharges and consequent great variations 
in flow. As the size of the drainage area increases, the possibilities of 
intense precipitation over the entire drainage area are greatly reduced, 
and with this increase floods in the main streams become correspond- 
ingly less in relative magnitude. 

(b) The fan arrangement of tributaries results in high flows reach- 
ing the main stream at the common center of discharge of the tributaries 
at about the same time, and causes congestion and consequent extreme 
flood conditions (Fig. 108, page 197), while a fern leaf arrangement of 
tributaries (Fig. 264) will in general result in less extreme floods. 

(c) The geographical location of the drainage area may have a sim- 
ilar effect. Should the drainage area lie in a direction parallel with the 
path of intense storms, the precipitation and flow may be greatly in- 
creased over those which occur where the area extends across these 
storm paths, and consequently commonly receive intense rainfall only 
over a portion of the area. 

The hydrographs of small areas often show the effects of heavy rains 
by an immediate and marked increase in the flow, as will be npted by a 
comparison of the hydrographs of Perkiomen Creek and the Kennebec 
River (Fig. 265, page 446). On drainage areas of small streams where 
pervious deposits largely obtain, the rainfall is rapidly absorbed and 
does not radically affect the runoff nor do these streams show greater 
fluctuations than larger streams : for example, compare hydrographs of 
the Coosa River and Nottingham Creek (Fig. 265). Large streams do 
not feel the immediate effect of rainfall on account of the time required 
for the runoff to reach the main stream. 

The flow of large streams is also modified by the fact that uniform 
conditions of rainfall seldom obtain on the entire area. On large 
drainage areas conditions of rainfall may prevail on one or more of the 
tributaries only, while on other portions of the drainage area no rain 
may be falling, with the result that the larger the stream the less be- 
come the extremes and the greater the uniformity of flow. In some 



Drainage Area. 



445 




Fig. 2G4. — Drainage Area of the Wisconsin River. 



446 



Stream Flow or Runoff. 



cases streams which are fed by mountain snows at particular seasons as 
for example, the Sacramento River (see Fig. 261, Hydrograph 20, 
page 439) or in some locations subject to occasional general heavy rain- 



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Fig. 2G5. — Hydro-graphs of Certain Rivers of the United States (see page 444). 

falls, as in the case of the Colorado River (see Fig. 259, Hydrograph 10, 
page 437), even large rivers may be subject to violent changes in runoff 
and to excessive flood conditions. 

200. Topography and Geology of Drainage Area and Channel. 

A. Topography of the Drainage Area — The important features are : 

(a) As to whether the surface is level or inclined, and the degree 

of inclination. 

(b) As to character of area, whether smooth or rugged. 



Drainage Area. 447 

B. Geology of Drainage Area: 

(a) Soils and rocks, their nature and whether pervious or im- 

pervious. 

( b) If pervious, whether such pervious deposits are (a) shallow 

or deep ; (b) level or inclined ; whether the outlet or point 
of discharge of the pervious deposits is (c) in the lower 
valley of the same river, or (d) in valleys of other rivers, 
or in the sea. 

C. Underflow Conditions. — As to the condition of the channel of 

the stream : 

(a) Whether pervious or impervious. 

(b) Whether the bed contains more or less extensive deposits 

of sand and gravel, permitting of the development of a 
more or less extensive underflow. 

(c) If impervious, whether the strata are cracked and fissured. 

A. Topography. — Mountainous topography favors orographic pre- 
cipitation for considerable distances from and on the windward side of 
the mountains or on the side toward which barometric changes of the 
atmosphere advance. On the other hand these same conditions give rise 
to a consequent diminution in precipitation on the leeward side of moun- 
tains. 

The topography of a drainage area has a marked effect on the quan- 
tity and intensity of runoff. Abrupt topography is essential to quick 
runoff, while a flat slope, even with the drainage area under similar geo- 
logical and surface conditions, is productive of slow surface flows and 
favorable to both seepage and evaporation. 

If the water stands on the surface of a comparatively level and pervi- 
ous deposit, or flows slowly across it, considerable opportunity is given 
for seepage into the soil and rocks of the drainage area ; whereas, if the 
surface is steeply inclined, a rapid flow of water over the same surface 
will materially reduce the quantity of seepage. 

With impervious deposits, gradient may only slightly modify the 
quantity of water entering the strata which, in arty event, may be in- 
significant. 

B. Geological Conditions. — Geological conditions are frequently of 
great importance in their influence on the quantity and regularity of 
runoff. If the geological deposits of the drainage area are highly im- 
pervious, the surface flow will receive and transmit the water into the 
mass only through the cracks and fissures in the rock. Pervious ma- 



448 Stream Flow or Runoff. 

terials, such as sandstones, sands, gravels and cracked or fissured rocks, 
induce seepage, retard runoff, and, if such deposits are underlaid with an 
impervious bed, provide underground storage which impounds water 
away from the conditions which permit evaporation, and hence tends to 
increase runoff and equalize flow. On the other hand, if such pervious 
deposits possess other outlets outside of the stream channel and drain- 
age area, they may result in the withdrawal of more or less of the seep- 
age waters entirely from the ultimate flow of the stream. Coarse sands 
and gravels will rapidly imbibe the rainfall into their structure. Fine 
and loose beds of sand also rapidly receive and transmit the rainfall un- 
less the precipitation is exceedingly heavy under which conditions some 
of it may flow away on the surface. 

Many of the highly pervious indurated formations receive water 
slowly and require a considerable time of contact in order to receive and 
remove the maximum amount. 

In flat, pervious areas, rainfalls of a certain intensity are frequently 
essential to the production of any resulting stream flow. In a certain 
Colorado drainage area, the drainage channel is normally dry except 
after a rainfall of one-half inch or more. A less rainfall, except under 
the condition of a previously saturated area, evaporates and sinks 
through the soil and into the deep lying pervious sand rock under the 
surface which transmits it beyond the drainage area. Such results are 
frequently greatly obscurred by the interference of other factors, such 
as temperature, vegetation, etc. 

The determination of the detailed geological conditions which may 
modify the resulting runoff from any drainage area, and the evaluation 
of the effect of such conditions on runoff, are practically impossible and 
can not be made with sufficient accuracy to furnish a safe basis for an 
estimate of the approximate results which will obtain therefrom without 
observations of the actual stream flow. The effects of such conditions, 
however, are important and sometimes furnish an explanation of quanti- 
tative differences in flow not otherwise explainable and often afford a 
warning of probable comparative differences in flows which must be ex- 
pected from the variation in the conditions that obtain. 

The difference in unit runoff of the Wisconsin River above Merrill 
and Necedah, Wisconsin (see Fig. 266, page 449), is probably due to 
the effects of the granite rocks above Merrill which produce a maximum 
runoff, while the pervious Potsdam deposits over the lower part of the 
drainage area and under the bed of the lower stream probably induce a 
considerable loss by seepage into that stratum and away from the 
channel. 



25 



Drainage Area. 449 

Jan., Feb Mar Apr May June Ju/y Aug Sept Oct. Nov Dec 




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Wisconsin River at Phine/ander-Dra/nage Area 832 Square Mi/es 




\ _~_ Wisconsin N/'ver af Mem'//- Drainage Area 26 ~30 Square Mi/es 



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Wisconsin Piver at Ki/bourn- Drainage Area 7800 5quare Mi/es 
Fig. 266; — Hydrographs of the Wisconsin River at Various Stations. 



Hydrology — 29 



450 Stream Flow or Runoff. 

C. Ground Water and Underflow. — Ground water proper flows un- 
derneath and at greater or less distance below the surface. Small 
streams sometimes occur in caverns and fissures in the rocks, particu- 
larly in the limestone regions. 

The ground water proper usually has outlets in the lower portions of 
the drainage area upon which it falls as rain, and appears as springs 
along the banks and in the bed of the stream channel itself and is usually 
the main source of supply for the dry weather flow. Deep seated ground 
waters which enter the pervious formations may follow such formations 
to distant outlets perhaps on other drainage areas or into the sea. 

Many streams occupy trenches, and occasionally broad valleys of 
considerable cross section, which are partially or largely rilled with de- 
posits of sand, gravel, silt, clays, etc. In such cases the pervious strata 
below water level are saturated and may transmit a considerable under- 
flow. The Rock river from Lake Koshkonong, Wisconsin, to Rock- 
ford, Illinois (see Fig. 220, page 374), flows over a preglacial drainage 
valley 100 feet or more below the present river. This channel carries a 
considerable underflow from which many private water supplies are ob- 
tained. This is also the case in many Western river channels which 
carry surface water only during storms, but water can often be ob- 
tained from wells in the dry bed. In the dry season the surface stream 
in such channels may disappear entirely and the underflow still continue, 
as in the case of the Arkansas River at Wichita, Kansas, Fig. 244, p. 409. 
Such flows may be of considerable importance in sustaining water sup- 
plies from wells constructed in such deposits for public and private pur- 
poses and for irrigation as in the case of the Gila River underflow in Ari- 
zona, Fig. 242, page 407. While considerable quantities of water are ob- 
tainable from such sources, the possibilities of such sources are fre- 
quently overestimated where cross sections and ground water slopes are 
comparatively small. In some cases the rivers have been forced out of 
their ancient beds which have been filled but still afford passages for 
more or less underflow which may then be diverted entirely away from 
the stream. (See Fig. 223, page 380.) 

201. Meteorological Conditions. — The important factors are : 

A. Temperature. 

(a) The annual and seasonal temperatures on the area, their 

duration and variation, and the resulting accumulation of 
snow and ice. 

(b) The relation of extreme low temperatures to the occurrence 

of precipitation, and the possibility of the freezing of 



Meteorological Conditions. 45 1 

ground surface at times of heavy spring rains, resulting 
in excessive runoff. 

B. Barometric and Atmospheric Movements. 

(a) Relations to paths of storm centers. 

(b) Effects of passage of barometric centers of pressure. 

(c) Winds resulting from barometric conditions. 

C. Evaporation. 

A. Temperature. — Temperature often has a marked effect upon run- 
off. Snow falling on a drainage area, ice formed from the rain on the 
area, and ice over the surface of water are temporarily stored and will 
be released only when the temperature rises. In high latitudes and high 
altitudes low temperatures are productive of storage in the form of ice 
or snow, and the advance of the spring season with its consequent in- 
crease in temperature is often productive of floods from such storage 
without accompanying adequate precipitation. (See Fig. 267, page 
452.) The saturated and frozen condition of the ground also fre- 
quently results in excessive floods from a comparatively small amount of 
precipitation where under other conditions the pervious drainage area 
would normally retain such rainfall without flood effects. 

The sudden freezing of streams may cause an abnormal but temporary 
decrease in flow even where the sources are not seriously affected. The 
friction of flow of a river under ice is considerably greater than with 
open water, hence when ice is suddenly formed on a stream, not only 
is a considerable quantity of water congealed and temporarily withdrawn 
from the runoff, but the river must rise and fill a greater cross section in 
order to overcome the extra friction caused by the ice formation. Sud- 
den temporary reductions of 50 to ys c /° m tne ^ ow °^ streams are some- 
times occasioned in this way, which is usually partially recovered within 
a few days after the advent of the cold wave. 

The occurrence, in high latitudes during periods of low temperature, 
of torrential rains such as occur, in summer seems to be physically im- 
possible on account of the small amount of moisture carried in the atmos- 
phere during winter periods. (Compare Figs. 65 and 67, page 120.) 

High temperatures, especially where accompanied by wind move- 
ments, also favor evaporation. 

B. Barometric and Atmospheric Movements. Winds: (a) It has 
been pointed out that the paths of cyclonic storms are favorable to pre- 
cipitation (see Sec. 92) and that the relation of such paths to the posi- 
tion and size of a drainage area under consideration may have an im- 



452 



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Fir.. 267. — The Relations between Stream Flow and Rising Temperatures. 



Meteorological Conditions. 453 

portant influence on the torrential character of the flow of the stream. 
(See Sec. 199.) 

(b) Large rivers fed by great lakes are sometimes subject to sudden 
changes in discharge on account of barometric movements increasing 
or decreasing the elevation of water at their heads during their passage. 
(See Sec. 54.) Such a change is shown by Fig. 55, page 102, re- 
produced from the graphical record of the U. S. Lake Survey gage, 
located at the St. Clair River. 

(c) The intensity and direction of the normal winds resulting from 
barometric movements or from local or seasonal conditions may have a 
considerably modifying effect upon the quantity of evaporation and, 
though sometimes insignificant, have a decided effect in increasing the 
amount of evaporation from exposed water surfaces, as the saturated 
air in contact with such surfaces is rapidly removed and fresh unsat- 
urated air is brought into contact with them. Where these water sur- 
faces are small and lie among the hills or are surrounded by forests, the 
effect of the wind on the same is greatly reduced and evaporation is 
less. Heavy and continuous winds by their effects on lake levels have 
a marked .effect upon the flow of the streams which drain the lakes. 
(See Sec. 53, page 98.) 

C. Evaporation. (See Sees. 67 to 79.) A large evaporation takes 
place from swamp and lake surfaces. In some localities this evapora- 
tion is fully equal to and in some cases even greater than the amount of 
rain that actually falls on the exposed water surfaces. If such areas 
occupied approximately the full drainage area, no runoff whatever would 
take place. While evaporation is a large item on exposed surfaces, the 
actual percentage of water surface on any drainage area is usually com- 
paratively small, and the evaporation is therefore not so large a factor 
when the entire drainage area is considered. Swamps and lakes, there- 
fore, tend to conserve and control the flood waters and undoubtedly in 
most cases add materially to the regularity of stream flow, although they 
frequently reduce its total annual amount. 

202. Surface Conditions. — The drainage area may be all or in part : 

A. Drained or undrained. 

B. Natural or cultivated. 

C. Bare or covered with vegetation, crops, grass lands or forests. 
Surface conditions have a marked effect on runoff, but such effects 

are not always obvious. 

A. Drainage. — The effects of lakes and swamps are discussed in Sec- 
tion 203, but the effects of the withdrawal of swamp area on stream flow 



454 Stream Flow or Runoff. 

are not fully understood. In general, drainage work practically affects 
surface storage only although occasionally ground storage may be 
slightly affected. Open drainage canals and ditches bring the surface 
flow more directly and quickly into the stream and thus undoubtedly 
tend to increase the flood height. Cultivation and subdrainage, how- 
ever, have an opposite effect as they improve seepage and ground storage 
conditions. 

B. Natural and Cultivated Areas. — Cultivation of the ground pro- 
duces two effects which influence runoff from a drainage area. The 
breaking up of the smooth surface of a field, especially in a semi-imper- 
vious deposit, undoubtedly will greatly facilitate the seepage of water 
into such deposits and will also decrease evaporation from the ground 
water (see Sec. 74, page 138). Cultivation, therefore, is frequently 
favorable to stream regulation. On the other hand, the cultivation of 
large areas that have previously existed in a natural condition has in 
some cases reduced to a considerable extent the water reaching the 
streams during the growing period. A compact sod on a considerable 
slope with large rainfall sometimes permits much greater runoff than 
is possible when the same area is broken and cultivated. 

While seepage and evaporation are greatly modified by geological con- 
ditions as noted in Section 200, the conditions of drainage and surface 
covering may be of equal importance. 

C. Forests and Vegetation. — A bare smooth surface is favorable to 
runoff and therefore to flood conditions. The presence of vegetation - 
on a drainage area may materially decrease the rapidity with which 
water flows therefrom and such vegatation may or may not be favorable 
to the uniformity of the flow of a stream. A surface covered with vege- 
tation may, to a considerable extent, delay the removal of rain during 
the smaller storm. The humus, due to forest growth, may form to 
some extent a minor storage which will prevent the immediate removal 
of the water of limited storms. When, however, the rain is extensive, 
the humus or covering of vegetation becomes saturated and the water 
then runs from the surface almost as freely as though no vegetation ex- 
isted. The effect, therefore, of vegetation on runoff is to retard the 
earlier flows from the surface which, however, may be delivered to the 
streams at a later period. Such conditions may be favorable or un- 
favorable to higher flood conditions according to the intensity of the 
storm and the discharging time and capacity of other tributary streams 
of the same drainage area. 

Of the amount of water actually held or retarded by vegetation, it is 



Surface Conditions. 455 

obvious that the larger portion may be taken up by the vegetation and 
used in vegetable growth and expired by the leaves. The retention of 
the water in this way will increase evaporation. While in a minor way 
this vegetation may be considered as regulating stream flow, it prevents 
a certain amount of precipitation which might otherwise flow away 
from ever reaching the stream. On an area of a pervious nature and 
with considerable gradient, the vegetation holding the water on the 
slope may assure a considerable extra amount of seepage which, with 
suitable geological conditions, may be returned to the stream through the 
ground water and thus assist in the regulation of the stream. Where, 
on the other hand, the deposits lie in a comparatively low gradient and 
are highly previous, the presence of vegetation on the surface will limit 
the flow of water into the underlying deposits and prevent the rapid 
seepage which would otherwise occur. Under such conditions the 
presence of vegetation on the drainage area will assure a loss to the. 
stream flow caused by the increase in evaporation and vegetable use. 

According to certain French measurements, 1 from 10 to 40 per cent 
of the rain falling on a forest never reaches the ground but is caught 
by the trees and re-evaporated. On the other hand, evaporation is 
greatly- reduced within the forest shade and the loss either from wet 
ground or water surfaces thus protected is much less than in the open 
field. The melting of snow is retarded by the shade of the forest and 
the same is true of ice in thickly forested swamps, but the delay in the 
melting of snow or ice is not sufficient to reserve the supply until needed 
in the extreme low water periods of August and September. 

Outside of the direct influence of forests on the immediate disposal 
of the rainfall, it must be noted that the roots from vegetable life pene- 
trating deeply into the ground take from the soil and the underground 
reservoirs much water which otherwise would ultimately reach the 
stream. After a considerable period of dry weather one has only to 
make a comparatively shallow excavation in the field and forests to ascer- 
tain how greatly the deep roots from the forest trees drain the soil of 
its water to considerable depths for the use of forest growth, and con- 
sume instead of conserve the supply they are said to store. 

Much stress is sometimes laid on the reservoirs provided by the for- 
est beds which are said to conserve the rainfall and to regulate runoff. 
Such reservoirs are largely ideal and are ordinarily of small relative im- 
portance. The investigator will search in vain in the forest bed for the 



1 Bulletin No. 7, Forestry Div. U. S. Dept. Agriculture, p. 131. 



456 Stream Flow or Runoff. 

stored water which is claimed to regulate and augment the flow of 
streams. 

There is no mystery to the engineer as to the actual reservoirs which 
supply the normal streams. A visit to the lakes and swamps will show 
a quantity of water therein contained which is manifest and not to be 
questioned. An excavation into the drainage area will uncover the 
underground sand and gravel and the water is there in great quantities. 
Its presence or importance can not be questioned. The surface waters 
from lakes and ponds, and the ground waters from sands and gravel 
are well known resources from which extensive public and private water 
supplies are often obtained, but the history of water supply engineering 
fails to furnish one instance where a forested area, as such, has been 
given any consideration as the possible source of a public water supply. 

There is no question but that forests and vegetation on abrupt slopes 
of certain character prevent denudation and hence may preserve certain 
deposits which act as underground storage. By the preservation of 
such vegetation, these deposits may be kept from being washed to river 
channels, and local conditions of storage are thus maintained better than 
would be the case when cultivation is attempted under improper condi- 
tions. In such cases, forests or other vegetation may have an important 
but indirect local effect on navigation and river improvements or main- 
tenance, but such efforts are purely local and do not in general appertain 
to all forest areas. 

203. The Character of the Storage on the Drainage Area. — The 
important factors are the nature and extent of 

A. Surface storage, consisting of lakes, ponds, marshes and 

swamps. 

B. Ground storage, consisting of gravel, sa-nd, and other similar 

pervious deposits. 

C. Artificial storage, consisting of waters impounded by dams for 

various useful purposes. 

The natural storage of any drainage area and the possibilities of arti- 
ficial storage depend principally upon its topography and geology. 
Storage equalizes flow, although the withdrawal of precipitation by snow 
or ice storage in northern areas often reduces winter flow to the mini- 
mum for the year. Both surface and subsurface storage sometimes 
hold the water from the streams at times when it might be advantage- 
ously used. Storage, while essential to regulation, is not always an 
advantage to immediate flow conditions. 

A. Surface Storage. — The presence of surface storage, ponds, lakes, 



St 



orage. 



«"7 



swamps, marshes, depends on incomplete drainage conditions and the 
existence of depressions with impermeable beds and restricted outlets. 
Such conditions tend to regulate the flood flows from drainage areas 
and to retard the flow of storm waters, delivering them more slowly 
than would occur from other areas. The effect of lakes and swamps 
is to reduce the flood peaks and prolong the high water period. Unless 
very considerable or unless augmented by extensive pervious deposits, 



48 



46 




44 



42 



40 



43 



46 



44 



42 



32 



30 88 86 8-4 82 80 78 

Fig. 26S. — Drainage Area of the Great Lakes. 



76 



their influence on the low flow of extreme dry periods is not particularly 
advantageous without artificial regulation. The evaporation from such 
swamp and marsh areas, and similarly exposed bodies of water, is con- 
siderable and reduces total runoff. 

The rivers flowing from the Great Lakes of North America are an 
important example of the effects of natural surface storage on the regu- 
lation and flow of streams. The ratio of lake surface to drainage area 
(see Fig. 268), on these areas is about 33 per cent, for the entire sys- 
tem, and the ratio of average annual discharge to mean annual rainfall 
is about 37 per cent. This is less than the average ratio of discharge 
to rainfall of many streams in their immediate vicinity, and the reduc- 
tion is doubtless due to the great evaporation from the free water sur- 
face of the lakes. 



458 Stream Flow or Runoff. 

Jan. Feb Mar Apr Mac/ June Jv/y Auy.^epf Oct Mok Dec Jan. Feb Mar Apr Flay 




f/udson f?/ver at Ftechan/cv///e,Necu York - Drainage Area 4SOO Sauare F7//es 



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Fig. 269. — Hydrographs of Certain New York Streams. 



Storage. 



459 



The effect of surface storage on the flow of streams is well shown by 
(Fig. 269, page 458), a comparison of the hydrographs of the Hudson, 
Oswego and Genesee Rivers of New York State. The Hudson River 
flows from a drainage area (see Fig. 270) having numerous small 
moraine lakes providing moderate storage. The drainage area of 
the Oswego River (see Fig. 271, page 460) has an unusual amount of 




Fig. 270. — Drainage Area of the Hudson River. 

storage in the numerous lakes of central New York. The Genesee 
River (see Fig. 2^2, page 461) has only a limited amount of surface 
storage. A part of the difference in the flow of these streams may be 
due to underground storage, although this factor is believed in these 
cases to be subordinate to surface storage. 

B. Sub-Surface Storage. — Extensive pervious deposits on a drainage 
area generally produce a high degree of regularity in the flow of a 
stream. On drainage areas where such pervious deposits are exten- 
sively developed, the rainfall, especially if the surface be uncovered by 
vegetation, is rapidly absorbed, becomes a part of the ground water, 



460 



Stream Flow or Runoff. 



flows slowly toward the stream and, dependent upon the character of 
the deposit, reaches the stream only after a lapse of days or perhaps 
months. As the ground water becomes filled the gradient becomes 
steeper and the rapidity of its flow is increased. Heavy rainfalls on a 




\c& t 








Fig. 271. — Drainage Area of the Oswego River. 

pervious drainage area therefore will considerably increase the velocity 
of the ground water flow and hence augment the flow of the streams to 
a greater extent during or following such periods. As time passes 
after the occurrence of rains, the gradient will slowly decrease as the 
water drains from the pervious deposits into the stream, the velocity 
and quantity of flow become less, and the stream flow gradually de- 
creases. The decrease, however, is not rapid and a sufficient quantity 
is often held in storage until further rainfalls augment the stored ground 
water and a^ain increase the stream flow. With high ground water, 



Storage. 46 1 

such a stream may frequently flow for several months without any ad- 
ditional rainfall, and the flow is commonly regulated to a greater de- 
gree by this means than by any other natural condition on the drainage 
area. The flow from such areas is usually a comparatively large per- 
centage of the total rainfall. 

Ground storage in gravels and sand, or other pervious deposits, re- 
moves to a considerable extent all of the water reaching them from the 
immediate influence of evaporation and stores them under the very best 
conditions for the future supply of the stream. 




Fig. 272. — Drainage Area of the Genesee River. 

The difference in the effect of surface and underground storage is 
quite well illustrated by a comparison of the Black and Wisconsin Rivers 
of Wisconsin, with the Manistee River of Michigan. (See Fig. 273, 
page 462.) The Wisconsin River drainage above Merrill, Wisconsin 
has numerous moraine lakes and several artificial reservoirs to store 
water for power purposes. (See Fig. 200, page 339.) The Black 
River above Neillsville, Wisconsin, has little storage. The Manistee 
River has little surface storage, but its drainage area is largely of sand 
and the regularity of the flow is remarkable. 

C. Artificial Storage. — Artificial storage created and controlled is 
usually surface storage and is open to the objections previously men- 
tioned. It has the advantage of permitting the use of the stored water 
when and as it is needed, and the entire withdrawal of the supply at 
other times provided the control is sufficiently extensive. Storage, 
when introduced on a drainage area, can be used for equalizing flow of 



462 



Stream Flow or Runoff. 



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Fig. 273. — Comparative Hydrographs of Certain Wisconsin and Michigan 

Rivers. 



Storage. 463 

the main stream only with certain points and purposes in view. Fre- 
quently, where water is stored for various purposes, such as navigation 
and power purposes, its use for one purpose is found to be antagonistic 
to other uses. 

Figure 274, page 464, shows the ideal regulation of the Hudson River 
based on a proposed extensive reservoir system and on the stream flow 
for the years of 1908 and 1909. It may readily be appreciated that the 
regulation secured by such means during a term of years will vary 
greatly, depending upon the increase or decrease in the annual runoff 
and on the distribution of the same. 

An example of the manner in which adequate storage facilities may 
reduce the flood peak is afforded by the Shoshone Dam near Cody, 
Wyoming. The normal flow of the river is discharged through two 
48-inch circular pipes at the base of the dam, which is 295 feet high 
from foundation to spillway, and impounds some 256,000 acre feet of 
water. As the flood waters due to the melting snow come down in 
June, the reservoir begins to fill and the discharge through the sluices 
slowly increases with the head, usually in August, the water in the 
river above the dam begins to grow less than the discharge through the 
pipes and by November the reservoir is again empty. The effect is 
to extend the high water flow over the entire summer and wholly to do 
away with the flood conditions as there has never been sufficient water 
to cause a discharge over the spillway. 

204. Artificial Use and Control of Streams. — When the waters of 
a stream are diverted or used, all or in part, an effect on the stream flow 
below the point of use is obvious. Such cases may include irrigation, 
public water supplies, and supplies for navigation canals. Furthermore 
the waters may be controlled : a. For water power purposes ; b. For 
storage to utilize flood flows during low water periods or to mitigate 
high water conditions in the lower river ; c. For the improvement of 
navigation by the construction of wing dams and jetties ; d. For pre- 
venting overflow by constructing dikes and levees which restrict the 
river to a channel section ; and e. For other public or private conven- 
iences or profit by various other encroachments upon the waterway often 
made without intentional interference with the regime of the stream. 

The construction of dams in a stream for power purposes affects the 
regularity of flow at every point below the dam, unless offset by a regu- 
lated discharge. The closing of a power plant, even with water going 
over the spillway of the dam, will cause a considerable decrease in flow 
below, as the pond above must fill before sufficient head is gained to 



464 



Stream Flow or Runoff. 




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Fig. 274. — Ideal Effect of Storage on the Flow of the Hudson River. After 
N. Y. State Water Commission, 1910. 

produce the same discharge. Numerous installations of this kind on 
a stream often seriously interfere with the regularity of flow below 
them, and may prove disadvantageous to navigation. (See Fig. 275, 
page 465.) 

The diking of channels to prevent overflow of lands often seriously 



Control of Streams. 



465 



affects flood heights at and above the lands diked, as the water which 
was formerly stored by overflow is forced through the restricted channel 
and more head is therefore necessary. The levees of the Missis- 
sippi River at and below Memphis, Tennessee, have caused the flood 
peaks at Memphis to rise more than eight feet above their former level. 

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Fig. 27G. — Obstructions in the Rock River at Janesville, Wis. 

It is necessary only to point out the radical effect of the diversion of 
water for irrigation, water supply and the feeding of navigation canals. 
Such effects are greater or less in accordance with the proportion of 
water removed from the stream, and the amount returned thereto by the 
seepage from irrigated lands, from irrigation ditches and the discharge 
of waste weirs and overflows from canals. 



Hydrology — 30 



466 Stream Flow or Runoff. 

Wing dams, jetties, and other navigation works are built to improve 
channel conditions without materially increasing the head at flood 
stages. The construction of bridge piers and abutments, the filling of 
low lands and other encroachments on the stream channel, while not 
intended to interfere with floods, often tend to produce higher flood 
peaks both by direct contraction of the channel and the opportunities 
of still greater contraction by the chance afforded for collecting and 
retaining drift. The obstruction of channels caused by the contruction 
of buildings over streams in cities where land values are high, some- 
times results in conditions which may prove serious in extreme floods. 
(Fig. 276, page 465.) Such obstructions in Mill Creek at Erie, Penn- 
sylvania, occasioned the great flood losses at that place in August, 1915. 2 

205. Conditions Favorable to Maximum Water Supply and Equal- 
ized Flow of Streams. — Case I. The following conditions are favorable 
to maximum equalized flow : 

A. Drainage Area : 

a. The drainage area must have an impervious bed of such a 

geological character that no water can sink into its mass 
and be conducted beyond the drainage boundaries to other 
areas, but it must be of such nature and capacity that all 
the precipitation received and not necessarily lost by evap- 
oration shall pass ultimately to the river channel. 

b. The surface slope must be slight so that little surface flow will 

take place even with intense precipitation. 

c. The larger the drainage area, the less the opportunity for a 

general intense precipitation which sometimes occurs on 
small areas, and the less the variation in flow under varying 
conditions of precipitation throughout the year. 

d. The temperature on the drainage area must be moderate, cool 

to reduce evaporating effects, and above freezing so that the 
surface may never become impervious through the forma- 
tion of ice, or receive precipitation as snow, with resulting 
loss from evaporation. 

B. Precipitation : 

a. The larger and more uniform the distribution of the annual 
precipitation, the greater the stream flow and the more per- 
fect its equalization. 



- Eng. News, August 12, 1915; also Eng. Record, August 14, 1915. 



Equalized Flow. 467 

b. The precipitation should be moderate in intensity so that it 

may be absorbed by a pervious surface and without sur- 
face flow, but never so light as to result simply in the mois- 
tening of the surface, with consequent loss by evapora- 
tion of the small precipitation thus received. 

c. For maximum water supply, maximum precipitation or high 

precipitation, with other favorable conditions, is essential. 
Whatever the precipitation may be, the maximum amount 
of runoff will result when the maximum proportion of the 
precipitation is preserved to the stream. For equalized 
stream flow, a uniform distribution of precipitation through 
each and every year is most favorable, and any variation in 
precipitation must be offset by inter-precipitation storage 
which, however, must not result in undue evaporation. 

C. Storage : 

a. In order that evaporation may be a minimum and hence the 

water supply a maximum, there must be no surface storage, 
and the river channel must be comparatively deep and nar- 
row, with a minimum exposed water surface. 

b. To provide storage and equalize the otherwise irregular stream 

flow due to the natural irregularity in the occurrence of 
precipitation, the impervious bed of the drainage area 
must be covered deeply with pervious sandstones or sands, 
not so coarse as to permit rapid flow through their struct- 
ure but coarse enough to receive the rainfall rapidly into 
their mass in order to avoid evaporating influences at the 
surface and to convey the waters deep enough so that cap- 
illary attraction will not draw them to the surface and sub- 
ject them to evaporation. The surface must be free from 
vegetation and be unobstructed by roots which would pro- 
duce similar effects. 

For conditions favorable to maximum runoff and equalized flow es- 
sentially as described above, consider a broad deep impervious rock- 
valley deeply filled with sand and gravel, the surface devoid of vegeta- 
tion and with the stream meandering through the center of the pervious 
plain. The rain falling on this area will sink rapidly into the pervious 
deposits and move slowly toward the river. Little of the water will be 
lost in evaporation because the rainfall will immediately sink below the 
surface and reach the ground water where it is not subject to evapora- 



468 Stream Flow or Runoff. 

tion effects. The great deposit of sand and gravel will store the water, 
retard its flow and permit it to move slowly towards the stream which 
will be fed with great uniformity, and while the ratio of rainfall to run- 
off in such a stram will be high, it will at the same time be distributed 
with considerable uniformity throughout the year and the stream will 
be perennial. These conditions will result in equalized flow, the degree of 
uniformity depending upon the perfection of development of the domi- 
nating factors mentioned above. There are few examples of extremely 
favorable conditions of this character. However, an illustration of the 
results of the occurrence of such factors to a high degree is shown by 
the hydrographs of the Manistee River of Michigan which flows through 
a sandy country where underground storage is highly developed. (See 
Fig- 273, page 462.) 

206. Conditions Favorable to Maximum Variation in Water Sup- 
ply of Streams. — Case II. For the maximum variation in the water 
supply of streams, the extreme case occurs when torrential flows, fol- 
lowing heavy precipitation, are succeeded by dry stream beds shortly 
after precipitation has ceased. The following conditions are favorable 
to maximum irregularities in flow : 

A. Drainage Area : 

a. In this case the conditions of maximum quantity and inten- 

sity of runoff require an impervious rocky drainage area. 

b. The drainage area must have a steep channel and abrupt 

slopes to the divide. The rock surface must be smooth, 
and both main and lateral channels unobstructed. 

c. No soil or mantle deposits, no vegetation, no storage, surface 

or subsurface, must exist to obstruct or delay surface flow 
if the maximum torrential stream flow is to result. 

d. The temperature must be mild to avoid storage in the form of 

ice or snow, but not too warm or evaporation will reduce 
runoff. 

e. The smaller the area, the more surely will areas of intense 

rainfall cover the entire drainage area and produce extreme 
conditions. 

R. Precipitation : 

a. The precipitation must be concentrated in a limited rainy sea- 
son with continuous downpours, followed by long continued 
droughts. Light rain would increase evaporation and de- 
crease the total discharge. 



Maximum Variation in Flow. 469 

A modification of the above conditions, leading in some cases to equal 
or more extreme conditions, might be occasioned by great deposits of 
snow during winter months followed by rapidly rising temperatures on 
the advent of spring when the combination of torrential rains and melt- 
ing snow might result in maximum runoff. 

Under the above conditions the heavy precipitation of intense storms 
accompanied perhaps by the waters from melting snows will flow rapidly 
and unimpeded down the smooth and abrupt slopes to the channel and 
rush down its steep gradient to its outlet, leaving a dry stream bed soon 
after the rain has ceased. The predominating influence of factors 
tending to irregularity of flow are shown by the hydrograph of the Gen- 
esee River, Figure 269, page 458. This example is not an extreme 
case, for this stream is seldom or never entirely dry ; its hydrograph 
shows the resulting conditions somewhat better than in the case of 
streams which entirely cease to flow at certain times in the year. 

207. Conditions Favorable to Minimum Runoff. — Case III. The 
following conditions are favorable to minimum runoff : 

A. Drainage Area : 

a. A pervious soil over a pervious rock bed from which the seep- 

age waters will be permanently lost to the stream. 

b. A low, flat drainage area largely covered by shallow swamps, 

filled with vegetation, from which the flow will be sluggish 
and the evaporation large. 

c. High temperature and strong winds, to increase evaporation, 

reduce humidity, and rapidly remove the humid atmos- 
phere. 

B. Precipitation : 

a. A small rainfall occurring in light showers, well distributed 
throughout the year. 

An excessive development of these conditions may result in no flow 
from a given area. 

Such conditions are not rare but as a rule are confined to very small 
drainage areas. There are numerous examples of such conditions 
found in Wisconsin and these examples are of two classes : 

1. Small sinks in sandy soil from which the rainfall partially evap- 
orates and partially sinks into the soil and flows to the main drainage 
channel of the general drainage area on which the sink is a local develop- 
ment. Similar sinks are also found in many limestone regions. In 
both cases seepage may be a considerable factor in rainfall disposal. 



470 Stream Flow or Runoff. 

2. Small depressions containing lakes which occupy a large propor- 
tion of the drainage area. In such cases seepage is a minimum and 
evaporation a maximum cause of rainfall disposal. 

208. Discussion of Extreme Conditions. — In Sec. 207, Case III, are 
illustrated the limiting conditions of no supply and this case needs no 
further discussion. Cases I and II embrace the extreme conditions of 
maximum water supply and uniformity of stream flow on the one hand 
(Sec. 205) and of maximum irregularity on the other hand (Sec. 206). 
In either case increased drainage area tends to greater regularity of 
flow but almost any other change or modification of whatever nature 
will disturb the condition and produce opposite effects in the two cases 
considered. The introduction of surface storage on these areas will in- 
crease evaporation in both cases, and hence will decrease total discharge ; 
but it will decrease regularity in Case I, while it will increase it in 
Case II. 

In Case I the occurrence of forests or vegetation of any kind on the 
drainage area will obstruct the pervious surface deposits and reduce 
the free access of water. The lighter rains will be kept entirely from 
the soil and evaporated from the surfaces of leaves. The forest bed 
will hold the moisture from the soil and conserve it for plant use. The 
roots will draw the moisture of the pervious soil from considerable 
depths. In each case a reduction in flow and a tendency to irregularities 
will result. In Case II the occurrence of forests on the impervious 
area, the forest bed, the vegetable fibre, the cracks opened by the roots, 
all offer both obstruction and limited storage and, while slightly reduc- 
ing the discharge, tend to equalize flow. 

LITERATURE 

RELATION OF RAINFALL AND STREAM FLOW 

Flow of the West Branch of the Croton River, J. J. R. Croes, Trans. Am. Soc. 

C. E., Vol. 3, p. 76, 1874; Vol. 4, p. 307, 1875. 
The Flow of the Sudbury River, Mass., A. Fteley, Trans. Am. Soc. C. E., Vol. 10, 

p. 225, 1881. 
Rainfall Received and Collected on the Watersheds of Sudbury River and 

Cochituate and Mystic Lakes, Dexter Brackett, Jour. Asso. Eng. Soc, 

Vol. 5, p. 395, 1886. 
Rainfall, the Amount Available for Water Supply, Desmond Fitzgerald, Jour. 

New Eng. W. Wks. Assn., 1891. 
Rainfall, Flow of Streams and Storage, Desmond Fitzgerald, Trans. Am. Soc. 

C. E., Vol. 27, p. 253, 1892. 
Rainfall and River Flow, C. C. Babb, Trans. Am. Soc. C. E., Vol. 28, p. 323, 1893. 
Relation of Rainfall to Water Supply, Charles E. Greene, Mich. Technic, Mich. 

Univ., 1895. 



Literature. 47 1 

Data Pertaining to Rainfall and Stream Floio, C. T. Johnston, Jour. Wes. Soc. 
Eng., Vol. 1, p. 297, June, 1896. 

Runoff of the Sudbury River Drainage Area, 1S75-1899, Inclusive, C. W. Sher- 
man, Eng. News, 1901. 

Relation of Rainfall to Runoff in California, J. B. Lippincott and S. G. Bennett, 
Eng. News, Vol. 47, p. 467, 1902. 

The Relation of Rainfall to Runoff, George W. Rafter, U. S. G. S. Water Sup- 
ply, Paper No. 80, 1903. 

Rainfall and Runoff on New England Atlantic Coast and Southwestern Colo- 
rado Streams, W. O. Webber, Jour. Asso. Eng. Soc, Vol. 31, p. 131, 1903. 

Rainfall and Runoff from Catchment Areas in New England, L. M. Hastings, 
Jour. New Eng. W. Wks. Assn., Vol 18, p. 32, 1904. 

Twenty Years' Runoff at Holyoke, Massachusetts, of the Connecticut River, 
Clemens Herschel, Trans. Am. Soc. C. E., Vol. 58, p. 29, 1906. 

Comparison of Rainfall and Runoff in the Northeastern United States, John C. 
Hoyt, Trans. Am. Soc. C. E., Vol. 33, p. 452, 1906. 

Length of Records Necessary for Determining Stream Flow, John C. Hoyt, 
Eng. News, Vol. 59, p. 459, 1908. 

Rain and Runoff near San Francisco, Cat., C. E. Grunsky, Trans. Am. Soc. 
C. E., Vol. 61, p. 496, 1908. 

The Yield of a Kentucky Watershed, G. L. Thon and L. R. Howson, Jour. Wes. 
Soc. Eng., Vol. 18, p. 634, 1913. 

FORESTS AND STREAM FLOW 

A. Favorable to Forest Influences on Runoff 

Decrease of Water in Springs, Creeks and Rivers, Contemporaneously with an 
Increase in Height of Floods in Cultivated Countries, Gustav Wix, Nos. 6 
and 9 Papers of Society of Austrian Engineers and Architects, 1879, 
Translated by M'aj. G. Wetzel, U. S. A., Washington Govt. Pt. Officers, 1880. 

The Influence of Forests upon the Rainfall and upon the Flow of Streams, 
Geo. F. Swain, Jour. New Eng. W. Wks. Ass'n, Vol. 1, March, 1887. 

Data of Stream Flow in Relation to Forests, Geo. W. Rafter, Ass'n C. E., Cor- 
nell Univ., Vol. 7, p. 22, 1899. 

Forest Influences, U. S. Dept. of Agric, Forestry Div., Bulletin No. 7, 1902. 

Forests and Water Supply, C. C. Vermuele, Ann. Report State Geol., New 
Jersey, 1899, p. 137. 

New Jersey Forests and Their Relation to Water Supply, C. C. Vermuele, Ab- 
stract of Paper before Meeting of the American Forestry Ass'n, New Jer- 
sey, June 25, 1900; Eng. News, July 26, 1900; Eng. Record, Vol. 42, p. 8, 
July 7, 1900. 

Forests, G. W. Rafter, Hydrology of the State of New York, Bui. 85, N. Y. State 
Museum, 1905. 

Saving the Forests and Streams of the U. S., Dr. Thos. E. Will, Jour. Frank- 
lin Inst. May, 1908. 

Conservation of Water Resources, Floods, M. O. Leighton, U. S. G. S. Water 
Supply Paper 234, 1909; also Rept Natl. Conservation Comm. Senate 
Doc. 676, 60th Cong. 2d Sess., Vol. 2, 1909. 



472 Geology. 



Surface Conditions and Stream Flow, Wm. L. Hall and H. Maxwell, U. S. Dept. 

of Agri., Forest Service Circular 176, Jan. 11, 1910. 
Influence of Forests on Climate and on Floods. G. F. Swain, Am. Forestry, 

Vol. 16, p. 224, 1910; also Eng. News, Vol. 63, p. 427, 1910. 

B. Adverse to Material Influences of Forests on Runoff 

Forests and Floods, Roberts, Am. Eng., April 11-25, May 2-30, June 6, 1884. 

Forests and Reservoirs in Their Relation to Stream Flow, Etc., H. M. Chitten- 
den, Trans. Am. Soc. C. E., Vol. 62, p. 245, 1909. 

Forests and Floods, Extracts from an Austrian Report on Floods of the Dan- 
ube with Applications to American Conditions, Lieut.-Col. H. M. Chitten- 
den, Eng. News, Vol. 60, p. 467, 1908. 

The Relation of Forests to Stream Flow, Editorial Eng. News, Vol. 60, p. 478, 
1908. 

Deforestation, Drainage and Tillage, with Special Reference to Their Effect 
on Michigan Streams, Robert E. Horton, Jour. Michigan Eng. Soc, 1908. 

The Relation of Forests to Stream Floxo, Maj. Wm. W. Harts, Extracted from 
Memoirs Corp. of Eng. U. S. A., Oct.-Dec, 1909, Eng. News, Vol. 63, p. 245, 
1910. 

A Report on the Influence of Forests on Climate and on Floods, Willis L. 
Moore, House of Rept., U. S. Committee on Agriculture, 1910; see also 
Eng. News, Vol. 63, p. 245, 1910. 

Report on Relation of Forests. to the Floio of the Merrimac River, Mass., Lieut.- 
Col. Edward Barr, Doc. No. 9, House of Rep. 62d Cong. 1st Sess., 1911; see 
also Eng. News, Vol. 66, p. 100, 1911. 

The Flow of Streams and the Factors that Modify it, with Special Reference 
to Wisconsin Conditions, D. W. Mead, Bui. No. 425, Univ. of Wisconsin, 
1911. 

Influence of Forests on Streams, L. C. Glenn, Eng. Assoc, of South, Vol. 21, 
p. 67, 1910. 



CHAPTER XVII 
VARIATIONS IN RUNOFF OR STREAM DISCHARGE 

209. Importance of a Knowledge of the Variation in Stream Flow. 

— The hydrographs previously discussed indicate ,in general great di- 
versities in the discharge : 

1. Of different streams. 

2. Of the same streams during different years. 

3. Of the same streams during different seasons of the same year. 
These differences have marked influences on the availability of each 

stream for utilitarian purposes depending upon these variations and 
the uses to which the stream may be applied. 

In order to make the use of a stream practicable for the purposes of 
a public water supply, navigation, water power or irrigation, it must 
be possible to secure a sufficient supply of water as needed and at a 
cost low enough to make the project financially feasible, otherwise the 
project should be abandoned. In every project the needs or demands 
for water and the supply are both more or less variable and are af- 
fected by the seasons, the climate, and by many other conditions. When 
only small supplies are to be taken from large lakes or rivers, the va- 
riations in runoff may be of little relative importance ; but when, as in 
many cases, the source of supply is to be developed to the maximum 
practicable extent, the problem of conserving and utilizing the irregular 
flow of a stream so that it may be made available at the time and in the 
quantity needed for a given purpose, is important. Every problem of 
this kind is essentially different from every other similar problem and 
must be considered by itself and in the light of all modifying influences. 
In considering such uses therefore any examples are only illustrative 
of special conditions and in every case the engineer must investigate 
for himself the nature of the demands of his project and the possible 
supply available from the particular source from which such demands 
must be met. 

210. Consideration of Public Water Supplies. — In the considera- 
tion of water supplies for most projects, not only the present but the 
future demands, must receive attention. The water needed for a 
public supply will increase with the growth of population ; it will vary 
from day to day with the season, with the humidity and with the tem- 
perature ; it will be less at night than in day time. In every problem 



474 



Variations in Runoff. 



these factors and often many others must be considered in connection 
with the source of supply and in the plans for its development. 

Fig. 277 shows the variation in both annual and monthly pumpage at 
Milwaukee, Wisconsin, together with the growth in population sup- 
plied. As Milwaukee draws its supply from Lake Michigan and that 
source for the purpose is unlimited, these variations are of importance 
only in the design of the system ; but if on account of gross pollution 
of the lake, Milwaukee was obliged to turn for a supply to upland 
streams, the future increased demands and their variations together 
with the variations in the flow of the stream considered would be of 



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great importance in considering the adequacy of such sources and the 
works needed to make the source useful to its maximum limits. 

211. Consideration of Supplies for Power Purposes. — For water 
power purposes studies of available supply and probable demand are 
not less important than for other projects. Fig. 278 shows the flow 
of the Peshtigo River, the power output of the plant (see Frontis- 
piece), the water stored and drawn from storage, the fluctuations in 
the reservoir surface and head, and the water wasted. To determine 
the practicability of utilizing the irregular flow of a stream for water 
power purposes, a study of its hydrographs, of the available heads, 
of the probable demand for power, of the available pondage or storage 
and of their economic relations is necessary. 



Supplies for Power. 



475 



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Variations in Runoff. 



212. Consideration of Supplies for Irrigation. — For irrigation pur- 
poses comparisons of supply and use are also essential. In many 
cases irrigation supplies are needed for only certain months in the year 



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B denotes average rain fa/I p/us average irrigation water 

The shaded areas denote average month/y rainfall during irrigation period. 

Fig. 279. — Monthly Variations in Water used on Three Irrigation Projects. 

and no water is used during the remaining months. Fig. 279 shows 
the variation in the monthly and annual use of water on three irriga- 
tion projects of the United States Reclamation Service for the years 
1912 to 1917 inclusive. On the Salt River Project in Arizona water 



Supplies for Irrigation. 



477 



is used to some extent during every month of the year, while on other 
projects water is used for only a portion of the year. 1 The demand for 
water will necessarily increase with the increase in area under cultiva- 
tion unless greater economies in the use of water can be successfully 
introduced or an increased rainfall is experienced during the irriga- 
tion season. The size of the project should be limited to the areas 
for which water can be made available. Fig. 280 shows the areas 
irrigated each year on these projects, the total amount of water used, 
and the rainfall during the irrigation season. An unusual rainfall 
em 1 — 



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79/2 /9/3 79/4 19/5 /9/6 /9/7 
Doffed fine denotes annua/ amount of wafer applied. 
So/id /ine denotes area irrigated each gear 

Fig. 280. — Water used and Area Irrigated on Three Irrigation Projects. 

on the Belle Fourche Project during the irrigation season of 191 5 
affected the amount of irrigation water used, as shown in Figs 279 and 
280. 

213. Consideration of Supplies for Other Uses.- — For navigation 
purposes water is used in northern climates for only certain periods 
during the open season when navigation is possible. For the remain- 
ing portion of the year ice prevents the operation of boats and the 
supply of water can be stored and held for navigation service if suffi- 
cient storage is available. In southern waters navigation may be con- 
tinuous throughout the year and a different demand results. In each 
case the effect of climate and other factors of demand change the 
problem, but in every case the problem is that of supply and demand 



1 Reclamation Record, November, 1918. 



478 Variations in Runoff. 

and involves the determination of the variations and the methods 
necessary to equalize them. 

214. Physical Variables in Engineering Problems. — In mathe- 
matics and other sciences certain principles defining the relations of 
cause and effect can be deduced which, when all extraneous influences 
can be eliminated, are absolute and universal. When, however, such 
principles are applied to engineering calculations the influences of 
varying physical conditions frequently make the application of such 
principles obscure, and the effects which will obtain cannot be ac- 
curately calculated from the simple principles which are obviously in- 
volved. Under these conditions a knowledge of the fundamental 
principles is still valuable for such principles frequently serve as the 
only guide for the engineer in his calculations even when they do not 
permit of an exact quantitative determination of results. To com- 
pensate for the unknown effect of the physical variables involved, 
factors of safety may be used in all engineering design. 

In the complicated problems of hydrology the underlying principles 
are obscure, for extraneous influences can seldom be so eliminated 
as to establish relations that are universally applicable. The pre- 
dominating influences are not always the same, and relations which 
seem obvious under one set of conditions appear absurd under condi- 
tions that are radically dissimilar. The determination of runoff is 
therefore not a simple problem but is in fact exceedingly complicated. 
Nevertheless, it is believed that by intelligent investigation and study 
such problems can be solved as accurately as most other engineering 
problems and that by the introduction of reasonable factors of safety, 
such solutions can be safely used as a basis for hydraulic design. 

The attempt in the following pages to outline underlying principles 
of runoff is for the purpose of calling the attention of the engineer to : 

1st. The complicated principles involved. 

2d. The danger of the unwarranted assumption of simple relations 
which do not exist. 

3d. The necessity of making an intelligent investigation of the many 
factors that modify the results which will obtain before any depend- 
able conclusions can be reached. 

The errors that often obtain in runoff estimates arise from the 
omissions of factors of safety and by attempts, often without proper 
investigation, to fix exactly the maximum or minimum flows or the 
mean daily, monthly or annual runoff. No engineering estimates 
can be made that are more than approximate, and allowances must be 
introduced to cover the ignorance of exact physical conditions. 



Physical Variables. 479 

In the design of structures the maximum load should seldom ex- 
ceed 1-3 or at most 1-2 of the normal limit of elasticity of the material 
used, for the maximum load is often merely an assumption, and the 
actual elastic limit of the material used is not accurately determined 
and both are in fact unknown. The structure to be safe must be de- 
signed for at least twice the strength that the assumption would seem 
to require. 

In runoff estimates it is impracticable in estimating water supplies 
to determine the probable minimum supply and to estimate it for safety 
at only one-half, or in flood protection to estimate the maximum that 
may possibly occur and then for safety to double the estimate. Such 
estimates would make hydraulic projects financially impracticable. 
It is, however, equally irrational to assume even the most dependable 
estimates of runoff as a safe basis on which to risk the lives or health 
of the public or the moneys of investors. Reasonable allowances must 
be made for safety, and the amount of such allowance must depend 
upon the risk involved and the seriousness of the consequences which 
will result from possible departures from the estimates made. 

215. Measurement of Stream Flow. 2 — The actual measurement of 
streamflow at the point where it is to be utilized and for a long term 
of years is the best possible information concerning its runoff. In 
few cases, however, when the utilization of a stream is first contem- 
plated can sufficient time be taken to secure long time measurements 
of flow. Nevertheless, it is important when such use is contemplated 
to establish immediately a gaging station, determine a rating curve, 
and secure continuous records for as long a period as possible in order 
to afford some basis for the comparison of the flow of the stream in 
question with the known flow of adjacent streams from which runoff 
data may be available for a longer period. 

The determination of the flow of a stream is an important but difficult 
problem. It is evident from the great variations in flow which take 
place from day to day that any. single measurement of the flow is of 
little importance by itself and has practically no significance. Fre- 
quent measurements should be made under different conditions of 
flow in order to determine the relations between gage heights and 
quantity, and an accurate long continued and continuous record should 
be kept in order to ascertain the variations in flow, the usual order of 
their occurrence, and the dependability of the stream for various 
purposes. Such a record may be made by single daily observations 



2 For complete discussion of this subject see River Discharge, by J. C. 
Hoyt and N. C. Grover. 



480 



Variations in Runoff. 



when the stream flow is fairly constant, but should be made by a con- 
tinuous recording gage whenever possible, especially with irregular 
streamflow so that all fluctuations of the surface elevation of the 
stream may be recorded automatically. (See Fig. 55, p. 102.) 

The uniform flow of water in channels of regular and fixed cross 
section and known conditions of roughness can be determined with a 
high degree of accuracy. In a straight reach of a uniform channel 
having a uniform slope (Fig. 281) and constant flow, the surface ele- 




Fig. 281. — Flow in a Uniform Channel. 

vation of the stream (ab) will be parallel to the stream bed (AB), 
and the gage height will always correspond with the same quantity 
of flow because the fall in the length of channel (1) will remain con- 
stant; hence the discharge (q) will always be constant in accordance 
with the well established principle 



in which 



«="-»V|t 



q = Flow in cubic feet per second 

a = Area of water section in square feet 

v = Mean velocity of flow in feet per second 

p = Wetted perimeter or wetted cross section in feet 

h = bx = Drop in feet in the length of reach 

1 = Length of reach 

c = A coefficient depending upon the roughness and character of 
the channel 
The relations of quantity of constant flow to height of water meas- 
ured by a fixed gage in any uniform channel can be represented by a 
uniform curve (Fig. 282 A) which becomes less regular in form with 
the greater irregularity in the controlling channel section, which con- 
trolling section may be some distance below the point at which the gage 
is established. (Fig. 282 B.) The shape of this curve can be deter- 



Measurement of Stream Flow. 



48 



mined experimentally by measurements at various stages of water in 
both regular and irregular channels. 

It is quite evident, however, that if the flow in the channel be in- 
creasing or decreasing (Fig. 281) the surface slope of the stream 
(a 2 b or a x b) will be measured by the fall (x 2 b or xjb) in the length (/) 




< 10 























































































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400 600 
Discharge 
A. Uniform Cross Section ana' Corresponding flaf/ntg Cur re 

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S.Irregu/ar Cross Section and Corresponding Tfat/ng Curve 

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C . Sat/s factory Rating Curve 
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Discharge-Thousands of Cubic Feet per Sec. Discharge-Thousands of Cubic feet per Sec. 

£T. Change in fiafing Curve due to Changed Section. f\Chanqe in Rat/ng Carve due to Tee in Section. 

Fig. 282. — Types of Rating Curves. 

Hydrology — 31 



482 Variations in Runoff. 

of the section and while the gage height (Bh) may remain the same 
for these conditions, the actual discharge through the section will be 
greater or less than with constant flow. 

216. Difficulties in Stream Measurements. — Unfortunately for the 
purpose of stream measurements stream channels vary radically from 
place to place in section, slope and character of bed, and the flow is 
not uniform but is constantly changing in quantity and consequently 
in slope. 

In practice, the flow of -streams at various times and with various 
heights of water only approximates that indicated by a rating curve 
because : 

1. The gaging stations may be improperly selected with regard to 
controlling sections, bends in the channel, obstructions to flow, etc., 
and thus be incapable of development as a suitable gaging station. 
(Fig. 282 D.) 

2. Measurements may be made with a rising or falling stream 
when the gradient is greater or less than that corresponding to a uni- 
form flow for the corresponding elevation of the stream. (See Fig. 
281.) 

3. The measurements from which the curve is established may be 
in error for accuracy can be attained only by experience and care. 

4. Cross sections unless in rock frequently change by scouring or 
may in any section be changed by the deposition of debris (Fig. 185, 
p. 327), thus altering the relation of gage height to discharge. (Sec 
Fig. 282 E.) 

5. The elevation of the water surface of streams may be greatly 
affected near the outlets by backwater from the rivers into which these 
streams flow and may at almost any point be affected by backwater 
resulting from jams of ice or logs, by the lodgment of materials or by 
the growth of aquatic grass and weeds which increase gage height 
while they reduce the corresponding stream flow. 

6. Even when the section chosen is fixed and satisfactory and the 
rating curve well established, only continuous gagings by a continuous 
recording gage will account for all the fluctuations in flow due to 
normal changes and artificial control of stream flow, and gagings taken 
only once per day may not fairly represent the flow of the stream for 
that day. (Fig. 55, p. 102.) 

7. Friction of flow is greater with an ice covered river, and a rating 
curve for ice conditions will differ greatly from the curve for an open 
channel. (Fig. 282 F.) In northern streams when ice is forming in 
a channel there is always a period of indefinite flow, for during the 



Measurement of Stream Flow. 483 

formation of ice the flows must necessarily change from those indicated 
by the rating curve for open conditions to those indicated by the rating 
curve for ice conditions, and the same change will take place on the 
breaking up of the ice in the spring. Such changes cover only a brief 
period, however, and are less important than other factors mentioned. 
Gagings made at dams are frequently in error on account of : 
i. Errors in discharge formula or discharge curve used. 

2. Leakage around or under the dam. 

3. Lack of continuous gagings with rapidly varying streams. 

For the above reasons many of the published gagings of streams 
are somewhat in error and consequently misleading. In many of 
the later stream gagings published by the Hydrographic Branch of the 
United States Geological Survey the relative reliability of the gagings 
is indicated. In all cases the gagings should be investigated before 
they are used as a basis for important conclusions. 

217. Runoff Data and Their Use. — The Hydrographic Branch of 
the U. S. Geological Survey has for many years been making observa- 
tions of runoff on various streams in the United States. 3 The number 
of gaging stations has gradually been increased as funds have become 
available, and in many cases the work has been considerablv exiended 
by State and private aid. In the earlier days of this work on account 
of inexperience and the lack of sufficient funds, many records were of 
more or less doubtful character, but some have been reviewed and 
rendered more accurate by later studies and investigations and have 
been republished in a corrected form. In spite of the increasing ex- 
tent of this work, it is frequently found when a new development is 
considered, that there are no data bearing directly on the project. 
Observations have often been made on neighboring streams or at other 
stations on the same stream, and conclusions must be drawn from the 
data available. Under these conditions it becomes imperative that 
runoff relations be investigated in order that such relations may be 
utilized to modify or confirm the available data for the use of the pro- 
ject under consideration. Unfortunately these relations are neces- 
sarily more or less discordant and inexact but this fact is common 
to all engineering data and should not stand in the way of an attempt 
to secure the best possible knowledge of the principles from which 
correct and conservative conclusions may be drawn. 

Where meteorological records and stream flow measurements are 
available the pertinent data most readily obtainable for an area arc in 



See Water Supply Papers of U. S. Geological Survey. 



484 Variations in Runoff. 

the order of their importance: runoff (local and comparative), mete- 
orological conditions (precipitation, temperature, wind velocity and 
humidity), physical conditions (topography, geology, surface and 
sub-surface storage) and surface culture (forests, vegetation, cultiva- 
tion, etc.). 

Data concerning stream flow can be obtained from various publica- 
tions and from the local Hydrographic office of the U. S. Geological 
Survey. Meteorological information can be obtained at the local 
Weather Bureau and from the publications of the U. S Weather 
Bureau. Some information concerning physical conditions on a drain- 
age area are often available in various State and United States Geolog- 
ical publications, but detailed data covering topography, geology and 
the physical condition of the drainage area as regards storage; soil, 
vegetation, etc., can be obtained only by observation and even then 
can be only generally known. 

The runoff data needed by the engineer in the solution of his various 
problems may vary greatly. A knowledge of the average annual 
streamflow is seldom sufficient even with large storage although the 
equalization of dry periods of several years by storage is sometimes 
possible. Even in such cases a knowledge of the distribution through 
the year is desirable at least to the extent of monthly flow. With small 
storage or with no storage available the flow of a stream from day to 
day becomes of great importance. 

In other problems the extreme conditions of drought or flood or the 
probable height of water levels are the controlling data and here local 
records are seldom sufficient, for considering the short time of observa- 
tion it is seldom safe to conclude that such extremes have been reached, 
and the engineer must gather information from many other besides 
local sources as a basis for conservative conclusions. 

For comparative purposes the flow from streams of known drainage 
areas must be available. It is not sufficient that the quantity of dis- 
charge of a certain stream be known, for such fact is of no value for 
comparative purposes unless the number of square miles of drainage 
area is also known. When comparative hydrographs of the monthly 
flows of a stream in cubic feet per second per square mile are to be 
used as a basis for stream flow computations, another doubtful element 
is introduced by estimating the drainage areas of the two streams that 
are to be compared. Engineers are cautioned against this source of 
error in various publications of the Hydrographic Branch of the U. S. 
Geological Survey. 4 



4 U. S. Geol. Survey, Water Supply Paper 353, p. 15. 



Runoff Data. 485 

"Even though the monthly means for any station may represent 
with a high degree of accuracy the quantity of water flowing past the 
gage, the figures showing discharge per square mile and depth of run- 
off in inches may be subject to gross errors, which result from including 
in the measured drainage area large noncontributing districts or omit- 
ting estimates of water diverted for irrigation or other use. 'Second 
feet per square mile' and 'runoff (depth in inches)' have therefore not 
been computed for streams draining areas in which the annual rainfall 
is less than 20 inches, nor for streams in which the precipitation exceeds 
20 inches if such computations might probably be uncertain and mis- 
leading because of the presence of large noncontributing districts in 
the measured drainage area, of omitting estimates of water diverted for 
irrigation or other use, or of artificial control or unusual natural con- 
trol of the flow of the river above the gaging station. All values of 
'second-feet per square mile' and 'runoff (depth in inches)' previously 
published by the United States Geological Survey should be used 
with extreme caution and such values in this report should be used with 
care because of possible inherent sources of error not known." 

In few cases are available maps sufficiently accurate to permit, with 
any great degree of accuracy, the determination of the drainage area 
of large streams. It is therefore evident that not only is measured 
stream flow s'ubject to more or less error but the drainage area from 
which it flows is known only approximately and when such data are 
used for comparative purposes, the exact drainage to which it is ap- 
plied is also somewhat uncertain. 

218. Variation in the Discharge of Different Streams. — It is evi- 
dent that if all things were equal the runoff or discharge per square 
mile of drainage area for all streams would be the same. In reality 
great differences occur in different. parts of the country in the various 
factors that affect runoff (Sec. 197) and in consequence there are cor- 
responding great differences in the flow of different streams. Some 
of these differences are shown by the hydrographs of Figs. 258 to 261, 
pages 436 to 439 inclusive, where rivers widely separated (Fig. 262) 
are each represented by a year of high flow and a year of low flow. It 
should be noted that these hydrographs show the discharge in cubic 
feet per second (hereinafter abbreviated as second feet or sec. ft.) 
per square mile of drainage area so that they are strictly comparative 
except that some of the hydrographs (Nos. 11, 12 and 13) are drawn 
to a scale ten times greater than the others. The high waters shown 
by these hydrographs vary from as high as 24 cu. ft. per sec. per square 
mile to as low as .38 sec. feet per square mile, and the low water flows 



486 Variations in Runoff. 

vary from as high as one sec. ft. per square mile to as low as .01 sec. 
ft. per square mile in the years of high flow. In areas widely separated 
such variations would normally be expected, and it is evident that there 
is little advantage in a comparative study of the flow of streams not 
contiguous and physically similiar as a basis for estimating the varia- 
tions in discharge which may be expected. 

In streams that are closely adjoining the comparative discharge may 
be expected to more nearly agree, but even under such conditions it is 
evident by a comparison of hydrographs that the physical conditions of 
the drainage area of various streams in the same state may be so greatly 
different as to result in large differences in their annual and seasonal 
discharges. This wide difference is shown by Fig. 269, page 458, 
which shows the comparative discharge of the Hudson, Oswego and 
Genesse Rivers in New York State. In the cases just stated the drain- 
age areas are not contiguous, but even when they are nearly so as in 
the case of the Black, the Wisconsin and the Rock Rivers of Wiscon- 
sin (Fig. 273), the conditions are frequently so different that both the 
high and the low stream flows differ radically in quantity, and the 
stream flows are not safely comparative. On the other hand it is true 
that when streams are adjacent and conditions are reasonably similar, 
a fairly close comparison exists in both the quantity and distribution of 
their annual flow (Fig. 283), and this agreement is frequently quite 
as close as is found in the comparison of flow at different stations on 
the same stream (Fig. 266, p. 449). and often within the limits of the 
factors of safety which should be applied to runoff estimates. 

2ig. Variation in the Discharge of the Same Stream. — The hy- 
drographs of Figs, 258 to 261 inclusive, show not only the variation in 
the flow of different streams but also in each case a hydrograph for a 
year of high flow and for a year of low flow is shown. From these 
hydrographs therefore an idea can be gained not only of the great 
difference in flow between different streams widely separated geograph- 
ically, but also of the great variations that occur in the runoff of in- 
dividual streams during different years. In long terms of years even 
greater variations in runoff sometimes occur than are there indicated. 
To obtain a full knowledge of the variations in the flow of a stream it 
is essential to study its hydrographs for a long term of years. 

The extreme maximum and minimum conditions of stream flow are 
even more rare in their occurrence than those of maximum and mini- 
mum conditons of annual rainfall, and it will be recalled by reference 
to Fig. 122, page 220, that the extremes' of annual rainfall at Boston 
that occurred in the fifty years prior to 1868 have not recurred in the 



Variations of a Stream. 487 

Jan Feb. Mar Apr May June Ju/y Aug. Sept Oct A/ov Dec 
20 




O.O 



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Dra/nage Area 24/3 Sq.Mi 




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Drainage Area &7Q 3a. Mi. 




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Drainage Area 6740 3q.Mt 

Fig. 283. — Hydrographs of Four Rivers in Wisconsin for 1908. 



488 



Variations in Runoff. 



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Variations of a Stream. 



489 



fifty years that have since elapsed. As stream flow depends upon the 
distribution of rainfall even more than on its total amount, and is also 
affected by various other factors as well, neither the maximum nor 
minimum stream flow will necessarily occur with extreme conditions 
of annual rainfall. It may be noted in this connection that the two 
most serious recorded floods on the Miami River of Ohio occurred in 
1805 and 1913, respectively, or one hundred and eight years apart, 
and it is quite conceivable that even more extreme conditions may 
occur in that stream at some future time. 



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Relative Discharge 

Fig. 285. — Relative Gage Heights and Discharges for Different Streams. 

Fig. 284, page 488, shows the gage heights of the Wisconsin River 
at Portage, Wisconsin, for forty years from 1878 to 1917, inclusive. 
Gage heights are not directly proportional to stream flow for the dis- 
charge increases much more rapidly as shown in Fig. 285, but the gage 
height frequently furnishes the information desired especially for re- 
clamation and flood protection work and is indicative of the great varia- 
tions which take place both from year to year and from season to 
season. In the study of Fig. 28^ the occurrence of years of low flow 
(1905 and 1910) should be noted, also the occasional years of high flow 
(1881 and 1884) an d of exceptional floods (1900 and 191 1), and the 
variation in the time and distribution of high and low water conditions. 

220. Seasonal Variations in Streams. — Each of the annual hydro- 
graphs which has previously been discussed shows great variations in 
seasonal runoff. Each hydrograph shows a period of maximum or 



490 Variations in Runoff. 

flood flow more or less pronounced and also a low water period during 
which the flow is reduced in most cases to but a small fraction of the 
maximum flow. The high water discharge is in general due to the oc- 
currence of heavy rainfall or in northern rivers to rising temperatures 
(Fig. 267, page 452) and the consequent discharge of waters that have 
been held in storage as ice or snow perhaps for several months and in 
many cases to a combination of both causes. The low flow is in gen- 
eral due to low rainfall or to the retention of the rainfall from the run- 
off by evaporation and transpiration which become more active during 
the growing season. The study of any long series of hydrographs of 
any stream (Fig. 284) shows that in general the periods of high and 
low water are somewhat constant but that great variations in their 
time of occurrences sometimes obtain. Any forecast of such occur- 
rence seems therefore quite indefinite and can be accomplished, if at all, 
only by a study of the rainfall-runoff relations of the past together with 
the many other physical conditions that modify such relations. 

221. Rainfall and Runoff. — As rainfall is the primary cause of run- 
off, the flow of a stream is naturally expected to increase or decrease 
with the rainfall, and in general such is the case ; but for the reasons 
considered in Sec. 118, there are many exceptions to this rule. At- 
tempts to establish any simple relations between rainfall and runoff 
have not met with encouraging success. 

The measurement of both rainfall and runoff is at best only ap- 
proximate. The impossibilities of making an accurate estimate of 
rainfall have been noted. (Sees. 101 and 102.) The difficulties in, the 
way of accurate measurements of runoff have been considered in Sec- 
tion 211. Even when the rainfall and runoff for the same period are 
determined with reasonable accuracy, the relations^ shown by their com- 
parison are more or less discordant. On a large drainage area the 
flow passing by the gaging station at any time is the net result of all 
the rainfall and other conditions that have obtained on the tributaries 
of this area for a considerable period prior to that date. The larger 
the drainage area and the greater the storage above the station, the 
greater the lag of the stream flow in relation to the rainfall that pro- 
duces it. Only on small drainage areas having relatively little storage 
is the effect of flooding rains realized almost immediately. On large 
areas the effects are not felt at distant outlets until days have elapsed, 
and they continue long after the rainstorm has passed. For these rea- 
sons the rainfall of one month usually affects the flow of the next 
month, and this becomes a large factor when the rainfall occurs late in 
the month. Where extensive storage obtains on a drainage area, the 



Rainfall and Runoff. 491 

effect of a rainstorm may continue for months. The selection of a 
water year instead of the calendar year for the study of rainfall-run- 
off relations is intended to obviate to some extent the lagging effects 
above described ; but as these effects are often greatly prolonged, there 
is no division of the water year which will obviate the effect except 
perhaps under conditions when there is little rainfall for several 
months as in the case of some localities on the Pacific Coast, and even 
here some of the streams still flow at the end of the dry season, show- 
ing that the effects of the rainy season still continue. See Rainfall 
at San Diego and San Francisco, (Fig. 130, page 234). 

222. The Lag of Stream Flow. — Fig. 286, page 492, shows by mass 
diagrams, a study of the relations of the rainfall-runoff conditions on 
the Wisconsin River above Necedah, Wisconsin, during 1904 and 1905. 
To construct such diagrams the rainfall from day to day during the 
year is added together as it occurs, and the accumulated sum is platted,, 
giving an upward inclined line from January 1 to December 31. The 
position of the line at any date shows the amount of rain that has fallen 
to that date, and the slope of the line indicates its intensity and distri- 
bution. The same method is used for indicating the amount and dis- 
tribution of the runoff or discharge of the stream during the year, and 
also the cumulative difference between the runoff and rainfall. This 
cumulative difference between rainfall and discharge represents evap- 
oration, transpiration, deep seepage and, when short periods are con- 
sidered, the temporary storage on the drainage area. This difference- 
between rainfall and discharge is often termed "evaporation;" but as 
this difference includes other losses as well, the term evaporation seems 
somewhat misleading and is here termed "retention" as opposed to. 
runoff. Retention is the amount of rainfall retained either perma- 
nently or temporarily from the stream and includes seepage and storage 
which may or may not ultimately be delivered to the stream. 

From the diagram for 1905 it will be noted that up to about March 27,. 
a large proportion of the rainfall had not reached the stream as runoff, 
but about April 1, on account of increased rainfall and melting snow 
and ice, the rate of stream flow increased and by May 1, the discharge 
had reached a total of about one inch more than the total rainfall ac- 
cumulated from January 1 to that date, showing that some of the rain- 
fall of the previous calendar year, held on the area as ice or storage, 
had finally reached Necedah. From May 1 to 18, rainfall of about 4 
inches occurred, about one inch of which was held for about 15 days 
before it reached Necedah, and on June 1 the runoff to date was about 
1.4 inches less than the rainfall. From June 4, the retention curve in- 



492 



Variations in Runoff. 









































































































































































































































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Fig. 286.— Mass Diagrams of Rainfall-Runoff Relations on the Wisconsin Rivef 
above Necedah, Wisconsin. 



Lag of Stream Flow. 



493 



creases much more rapidly than the discharge, as evaporation and trans- 
piration were active. Every depression in the retention line shows a 
delivery to the streams of water that has been held on the drainage area, 
and indicates the lag relation of the rainfall to the runoff. The mass 



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/fi4^d 7 <? S fO // /2f3*4/5 /6[/7/8/9202l 22232425262728S3303I 
O&fober /&// 

Fig. 287. — Advance of Flood Wave on the Wisconsin River. 

curves for 1904, show more clearly the delivery of retained waters. 
From these curves it will be noted especially that the heavy rains from 
September 1 to October 10, 1904, did not increase the rate of flow of 
the stream at Necedah until about October 12, but that from October 
10 to December 15, about 1^2 inches that had been held in storage was 
delivered to the stream. 



494 Variations in Runoff. 

223. The Retardation of Flood Waves. — Another illustration of 
the lag in runoff is shown by Fig. 287, page 493, which shows the ad- 
vance of a flood wave down the Wisconsin River from Rhinelander to 
Muscoda (Fig. 264, p. 445). This flood was caused by the storm of 
October 2 to 6, 191 1 (Fig. 322, Sec. 246). Rhinelander is below the 
lakes of the Wisconsin drainage area. In this area there is consider- 
able natural storage and also some artificial storage which has been 
created for power purposes. At Rhinelander there was little rise in 
the waters as the flood waters had been impounded, but below that point 
the flood wave accumulated from the lower tributaries became later 
and later as it proceeded down the river. At Necedah the flood wave 
was about four days later than at Merrill which is 151 miles farther up 
the river ; while at Muscoda, 278 miles below Merrill, there was a lag 
of more than seven days. It is evident that in considering rainfall- 
runoff relations this lag in the effects of rainfall must be considered. 

224. Effects of Storage on Runoff. — The effects of storage on run- 
off as shown by the mass curve of retention has been noted. Mr. C. B. 
Stewart 5 has determined that on some parts of the Upper Wisconsin 
River rainfalls of from 4 to 6 inches in the summer months will affect 
the stream for about five months in the approximate proportions of 
°5%> 19%, 10%, 4% and 2% of the total resulting runoff. Any meas- 
urements of such effects cannot be more than approximate and apply 
only to the individual drainage areas for which they have been deter- 
mined. The method of study used by Mr. Stewart was as follows : 

"Referring to the year 1907 (see Fig. 288) , the ordinates to the curved 
lines, starting with the given average monthly runoff and drawn down- 
ward and to the right, represent approximately the rates of runoff, if 
no rain should occur subsequent to the month for which the respective 
curves, representing the underground flow was determined as follows : 
In September, 1907, the average monthly rainfall was 6.08", 1.88" above 
the fourteen year average. The heavy rains were distributed over a 
period of about a week near the middle of the month, the heavier rains 
at single stations being about 4.6 inches. 

"The rainfall in each of the months, October, November and Decem- 
ber, was very small, amounting to 0.87", 0.69" and 0.42" respectively. 
The maximum daily rainfall at any one station in October and Novem- 
ber was about 0.40", with rains at other stations on or about the same 
dates averaging about 0.20". The maximum rainfall in December at 
any one station was 0.30", with rains at other stations averaging about 



5 Storage Reservoirs, by Clinton B. Stewart, Wisconsin State Board ' of 
Forestry, 1911. 



Effects of Storage. 



495 



o. 10". The amounts and distribution of the rainfall in these months 
was such that very little runoff could have resulted therefrom. Esti- 
mating the probable values for the runoff from these small rains, the 

Variation offlcfua/ Rain fa// from /4 Year Aire rage f/pove Merril/ 
+0.53 -045 -003 +O.06 -f.47 -/.I7 ~ /Z5 -O.74 +1.83 -2.07 -J.20 -0.59 

FPainfa/l Deficiency from Jan I, from 14 Year Average 
+0.53 +0.08 +OOO +0.06 -1.41 -Z.S8 -3.83 -4.57 -2.69 -476 -5.96 -6.55 




Jan. feb Mar flpr May June Ju/y f/ua Sept Ocf Nov Dec 
Fig. 288. — Ground Flow on the Upper Wisconsin River. After C. B. Stewart. 

curve A H may be drawn. Ordinates to this curve at points A, C, E, 
etc., would represent with reasonable accuracy, the runoff for the cor- 
responding months of September, October, November, etc., if no rains 
had occurred subsequent to September. The ordinates to the curve 
I H 1 , similar in form to A H, at I, B, D, F, etc., would represent the 
runoff for the corresponding months of August, September, October, 
November, etc., if no rains had occurred subsequent to August." 

Similar studies to those of Mr. Stewart are the basis of the ground 



496 



Variations in Runoff. 



flow diagrams of Mr. C. C. Vermuele (Fig. 289), which he used to 
calculate the dry weather flow of streams from estimated depletions 
of the ground water. Vermuele found that the flow with full ground 
water in Eastern streams was in general two inches per month, and that 
when the depletion of the ground water occurs the monthly ground 
flow would vary with the average depletion for the month (Sec. 232 ). 
Curves of similar import are used by Professor Meyer as a basis for the 
calculation on ground flow (.Sec. 234). 



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Fig. 289.- 



Average Month/y Dap/et/on of Ground hfatei — Inches. 

-Grounds Flow Curves of Eastern Streams. After C. C. Vermuele- 



225. Variation in Annual Relations of Rainfall to Runoff. — Taking 
into account the lag of streamflow due to surface and ground storage, 
it is not to be expected that any close agreement will be observed be- 
tween rainfall and runoff for the same period, and the shorter the 
period and the larger the drainage area, the more discordant the rela- 
tions which must be expected. Fig. 263, page 443, shows the relations 
of total annual rainfall to total annual runoff on four streams in which 
the data for various years are arranged in the order of the magnitude 
of the annual rainfall. From this diagram it will be seen that in general 
the annual runoff has increased with the annual rainfall but that in each 
case there are exceptions more or less radical. In such cases various 
influences have intervened and have overcome the effects on runoff due 
to the changes in rainfall conditions. 

If a diagram be drawn (Fig. 290, p. 497) on which the annual rain- 
falls be represented by abscissas and the runoff by ordinates, a 45 ° line 
drawn from the zero point will represent 100% of the rainfall that 
might run off from a steeply inclined impervious drainage area, such 
as a slate roof. On account of the various losses which modify and re- 
duce runoff, the points indicating the relations of annual rainfall to an- 
nual runoff will fall considerably below this line. 

If it is assumed that retention remains fairly constant, all observa- 



Rainfall — Runoff Relations. 



497 



tions should fall upon a line drawn parallel to the 100% line and at a 
vertical distance therefrom equal to the average annual retention. In 
this case the horizontal or vertical distance between the inclined line 
and the 100% line represents the average annual retention, and the 
distance from the inclined line to the base represents the varying annual 
discharges. On this basis, the discharge would apparently be zero 
should the rainfall equal only the average retention. Where annual 
rainfalls decrease to this extent, it is found that some runoff usually 


























































































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Annual Rainfall- Inches. 
A- tjpprox imate Limits of Maximum Runoff 



o 10 20 so 40 SO 

/Jnnual Rainfall- Inches. 

B- Approximate Limits of Minimum Runoff 



Fig. 290. — Examples of Extreme Annual Rainfall-Runoff Relations, 
occurs when the rainfall is below the mean annual retention so that the 
general relations at these lower limits would be better represented by a 
curved line which becomes tangent to the base line at a point perhaps 
equal to about one-half the amount of the average annual retention. 

Long series of observations on many streams show that in general an 
annual rainfall of at least five inches is necessary to produce runoff 
even from small drainage areas with mountainous topography, while 
with broad valleys and gentle slopes, no runoff will occur with an an- 
nual rainfall of less than than io to 15 inches. This statement is some- 
what misleading as much depends upon the annual distribution and in- 
tensity of the rainfall so that the limits named are but roughly ap- 
proximate. When the annual rainfall becomes more than the mean 
annual retention there is an increase in runoff more nearly proportional 
to rainfall and in general this increases with the slope of the area. 

Curves drawn to represent mean annual rainfall runoff relations 

will begin with their zero at the limiting annual rainfall at which no 

runoff will occur and, in general, will run nearly parallel with the 100% 

line after the rain exceeds an amount perhaps double this limit. Re- 

Hydrology — 32 



498 Variations in Runoff. 

tention might be expected to increase with rainfall, for the more rain- 
fall the greater the opportunity for loss through evaporation, trans- 
piration and deep seepage. The consequence of increased rainfall, how- 
ever, is high humidity and reduced temperatures which have a tendency 
to diminish these losses. In general, practical results lie between the 
one extreme where the normal retention remains almost constant 
(Fig. 290 A) and the other extreme where the annual retention in- 
creases with the annual rainfall more rapidly than the increased runoff 
(Fig. 290 B). In both these cases it is important to note that runoff 
appears as a residual after the demands of temperature, evaporation and 
deep seepage are supplied. 

226. Approximating Rainfall-Runoff Relations. — Fig. 291 A shows 
the relation of annual rainfall to annual runoff of the Merrimac River 
above Lawrence, Massachusetts, for 36 years. The mean rainfall for 
this period was 41.49 inches, the mean runoff 20.06 inches, and this point 
is platted on the diagram in the center of gravity of the 36 years obser- 
vations. The inclined lines on the diagram radiating from the left 
lower corner indicate the varying percentages of the rainfall appearing 
as runoff. The average percentage of runoff, is 48.6% of the rainfall 
but the extreme variations are from 32.2% to 61.9%. Hence, if the 
discharge had been estimated on the basis of the mean percentage it 
would have been 51% too high in one case and 21.5% too low in the 
other. The line of mean annual retention is drawn parallel to the 
ioo c /o. If estimates of annual flow of the Merrimac River were made 
on the basis of this line, the extreme variation from actual flow would 
be 27.5% too high in one extreme and 25.3% too low in the other ex- 
treme. The latter estimate agrees with the facts somewhat more closely 
than the percentage estimate but both are considerably in error, and in 
the consideration of the rainfall-runoff relations of many drainage 
areas the errors in either method would be much greater than here in- 
dicated. (Fig. 291 B.) This variation is, however, sometimes well 
within the limits of the factor of safety which should be allowed in 
such estimates. 

If on these diagrams are shown not only the centers of gravity of all 
observations but also the center of gravity of the groups of observa- 
tions both greater and less than the mean, rainfall and runoff being con- 
sidered, lines to represent the mean rainfall-runoff relations with 
greater accuracy can be drawn through the center of gravity of the en- 
tire group and approximating the centers of gravity of the sub-groups. 
The angle of these lines with the base will usually be less than the 45 ° 
line of Fig. 291 A as is shown by the broken line in Fig. 291 C (after 
Rafter). 



Rainfall — Runoff Relations. 



499 



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Rain fa// in Inches 
C. Croton R/ver, A/ew rork-/877 to /899. 

Fig. 291.— Annual Rainfall-Runoff Relation on Three Rivers of Eastern United 

States. 



500 Variations in Runoff. 

Diagrams to fairly represent mean annual relations must differ with 
various conditions on each particular drainage area and will therefore 
vary somewhat with every stream. C. E. Grunsky has given the fol- 
lowing rule for roughly approximating the runoff from a drainage 
area. 

"The percentage of the annual rainfall, when less than 50 inches, 
which runs to the stream, is equal to the number of inches of rain. 
When the annual rain exceeds 50 inches, 25 inches thereof goes to the 
ground (evaporation) ; the remainder is runoff." 

This statement may be useful for readily keeping in mind the general 
form of a mean runoff curve, but it will hardly be useful for even the 
rough estimates for which it was designed, except under special con- 
ditions, as will be noted by reference to Fig. 292 on which the curve rep- 
resenting this rule is shown (as Curve No. 4) in comparison with other 
curves suggested by Mr. Grunsky and others for special areas. In this 
figure are also platted two extreme cases of streams of high and low 
runoff. Curve No. 1 shows the mean annual rainfall-runoff relations 
on the Salt Spring Valley. This is a drainage area of 25 square miles 
tributary to the San Joaquin River and flowing from the west foothills 
of the Sierra Nevadas in Calaveras County, California. These data 
were corrected by Lippincott and Bennett 7 for both rainfall and runoff. 
This curve represents an extreme condition of high runoff. Curve No. 
8 shows the mean annual rainfall-runoff relations of Boulder Creek 
with about 12 square miles drainage area and a mean altitude of 5500 
feet above Cuyamaca Reservoir in San Diego County, California. This 
area represents an extreme condition of low runoff. In both cases the 
annual relations are also platted on the diagram to show the considerable 
annual departures from the mean curves. These curves and others 
shown on Fig. 292 are listed on the diagram, but the annual departures 
from the other curves are not shown as further data would lead to con- 
fusion. In examining this diagram it should be noted how widely the 
observations of individual years depart from the curves which repre- 
sent mean annual relations and how impossible it is to use such curves 
as a basis for even approximately estimating the probable annual runoff 
from rainfall records of areas where different physical conditions obtain 
Engineers of considerable experience in other matters have sometimes 
used such curves as a basis for water supply estimates on projects in- 



e Rain and Runoff near San Francisco, California, by C. E. Grunsky, Trans. 
Am. Soc. C. E., Vol. 61, p. 514. 

" The Relation of Rainfall to Runoff in California, by J. B. Lippincott and 
S. G. Bennett, Eng. News, Vol. 47, p. 467. 



Rainfall — Runoff Relations. 



50 




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502 Variations in Runoff. 

volving large investments, although the curves are designed to show 
only probable mean relations for areas having certain special local 
characteristics. This illustration of misapplication of data should 
emphasize the danger of the use of either diagrams or formulas with- 
out a clear understanding of both their origin and meaning. 

227. Percentage Estimates and Empirical Expressions. — A method 
of estimating runoff presented by Mr. C. C. Babb 8 , involved the deter- 
mination of the average annual percentage of rainfall which appears as 
runoff as a basis for estimating annual runoff, and the use of the average 
percentage of annual flow occurring monthly as a basis of estimating 
monthly stream flow. The previous diagrams, showing the great depart- 
ure of different years from the mean annual relations (Fig. 291, page 
499) and of different months from the mean monthly relations (Fig. 295, 
p. 506) are sufficient evidence to show the futility and danger of this 
method for any but the roughest approximation for runoff. The 
method proposed by Mr. Babb is not sufficiently accurate to indicate 
even the approximate means of the flows of streams that are closely 
adjoining but which possess characteristics different from those for 
which he gives data. 

In Section 118 attention has been called to the fact that the division 
of the calendar year may not properly correspond to the division of the 
year best suited to the study of rainfall-runoff relations. The late 
George W. Rafter selected a water year from December 1 to Novem- 
ber 31 as the proper period for the study of Eastern streams and en- 
deavored to express the annual rainfall-runoff relation by an exponen- 
tial equation (No. 2 Fig. 292) which may possibly fit the varying an- 
nual relations in each particular case more accurately than any other 
expression. 

With curves such as are shown in Figs. 291 and 292, should the actual 
relations correspond with the assumptions used in any particular case, 
the point for such year would fall directly on the assumed line, but the 
annual relations will usually depart somewhat from this mean relation, 
and the amount of the departure will indicate the effect of the distri- 
bution of rainfall and of other factors which always modify these rela- 
tions. Occasionally a series of observations may agree closely with 
the assumptions used but in general the divergence is so marked as to 
render the mean relations very discordant and of little practical value 
as a basis for closely approximating runoff under conditions of rainfall 
for which no runoff observations are available. Such studies are of 



3 Rainfall and River Flow, by Cyrus C. Babb, Trans. Am. Soc. C. E., Vol. 28. 
page 323, 1893. 



Empirical Expressions. 



503 



considerable importance, however, as they show in a general way the 
effect of the local condition on the runoff of a particular drainage area 
and afford a basis for the estimate of average conditions on similar 
areas, which is at least better than can be made without such studies. 
Such studies further serve to warn investigators of the marked de- 
partures from such means that will certainly obtain in every drainage 
area. 



&8 






Merrimac River Drainage Area 

Mean Discharge at Lawrence Mass achusetts _ 
Average Mean Rainfall from W S. Paper '4J5 
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Mean Discharge of Riverside Alabama 

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Red River of the North Drainage Area 

Mean Discharge of f\ rargo North Dakota 
Average fv?eon Rainfal l I \a f fight Stat/ona 




Jan Deb Mar Apr May JunJu/y Aug Sept Oct Nov Dec. 



Fig. 293. — Average Distribution of Rainfall and Runoff Throughout the year 

for Various Streams. 



228. Variations in Periodic Rainfall and Runoff Relations. — As 
would normally be expected from the previous discussion, the rainfall- 
runoff relations for monthly or seasonal periods are even more erratic 
than those for the annual period. Temperature and vegetation in- 
crease with the summer months, and a greater proportion of the rain- 
fall is lost in evaporation and transpiration and therefore retained from 
the stream flow. The average seasonal rainfall-runoff relations of four 
streams are shown in Fig. 293. On the Merrimac River the mean 
maximum discharge is in April when the winter storage is delivered as 
runoff, and July, the month of maximum rainfall, has nearly the min- 



504 



Variations in Runoff. 



25 



Jan F eb. flar Apr May June Ju/y Auq Sepf Oct Nov Dec. 




Fig. 294.— Rainfall and Stream Flow for Four Years on the Wisconsin River. 

imum runoff. On the Coosa River the maximum rainfall and runoff 
occur in February and March, but the high rainfall of July shows com- 
paratively little effect on the stream flow. In each case the area below 
the line of runoff shows the mean annual discharge while the area be- 
tween the rainfall and runoff curves shows the mean annual retention. 
Fig. 294, page 504, shows four annual hydrographs of the Wiscon- 



Periodic Rainfall — Runoff Relations. 505 

sin River on which are also platted the mean daily rainfall on the area 
above the gaging station. The small rainfalls of March which precede 
the high water periods of April and May should especially be noted. 
The comparatively small effects of the large summer rainfalls on the 
flow of such periods should also be noted. 

In monthly periods the lag of the streamflow and the effect of other 
factors in general produce very discordant relations between the rain- 
fall and the resulting streamflow. Runoffs of more than 100% of the 
rainfall for the monthly periods become common in such comparisons 
on account of the effect of the rains of previous months. Fig. 295. 
page 506, is a study of these relations for monthly periods for three 
small streams near Philadelphia, Pennsylvania. A 45 ° line drawn from 
the lower lefthand corner of all such diagrams would indicate 100% 
rainfall-runoff relations, and discharges of more than 100% are found 
to be common for the first four months of the year. During May to 
August, inclusive, transpiration and evaporation are at their maximum 
and the proportion of runoff decreases, but even during May and August 
single instances are found when the runoff greatly exceeds the rainfall. 
This is, of course, due to heavy rains near the close of the preceding 
month and to low rainfalls for the month considered. For October to 
December, inclusive, the ratio of runoff to rainfall in general again in- 
creases on account of the reduction in evaporation and vegetable trans- 
piration, but the relations at best are discordant and not adapted to 
practical use for even approximate estimates of monthly flow. 

229. Rafter's Curves of Periodic Rainfall-Runoff Relations. — 
Rafter 9 found that monthly relations of rainfall to runoff were too dis- 
cordant to be used for streamflow estimates, but divided the water year 
from December 1 to November 30 into the following periods : 
December-May, Storage Period. 
June-August, Growing Period. 
September-November, Replenishing Period. 

He endeavored to show that when rainfall and runoff are considered 
for these periods the relations may be fairly Avell represented by curves 
which may be established for each stream. Fig. 296 is a reproduction 
of Rafter's diagrams for the Sudbury River rainfall-runoff relations 
for these three periods. 

On this diagram are shown, the mean line of retention for the period 
CC, a more rational line of relation GG drawn approximately through 



The Relations of Rainfall to Runoff, by George W. Rafter, W. S. Paper 
No. SO, U. S. G. S., also Hydrology of the State of New York, by George W. 
Rafter, Bui. 85, N. Y. State Museum. 



506 



Variations in Runoff. 













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Fig. 295.- 



-Monthly Rainfall Runoff Relations for Three Small Streams Near 
Philadelphia. 



Periodic Rainfall — Runoff Relations. 



507 



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Fig. 29G. — Rainfall-Runoff Relations on the Sudbury River for the periods of 
the Water Year. After George W. Rafter. 



508 Variations in Runoff. 

the center of gravity of the group, and subgroups and the curve RR 
drawn by Rafter as expressing his conclusions of the nearest approx- 
imation to these relations. The diagram shows, however, no closely 
concordant relations. 

230. Discordance in Rainfall-Runoff Relations. — It is evident from 
previous discussions that there exists no simple relations between rain- 
fall and runoff from which either monthly or annual stream discharges 
can be calculated with any great degree of accuracy from the known 
precipitation. The reasons for this are quite obvious. Runoff should 
be regarded as the overflow or residual remaining after various other 
demands are supplied and not as a proportion of rainfall. In general, 
the amounts of the rainfall which are retained from the runoff and are 
lost by evaporation, transpiration and deep seepage, are more constant 
in quantity than the runoff. Estimates of runoff calculated as equal to 
the rainfall minus a constant or increasing loss which will vary with 
different drainage areas, are more nearly in accord with the actual oc- 
currences than are estimates based on fixed percentages as has been 
shown in Sec. 214. Such methods of expressing runoff are illustrated 
by Figs. 290 and 291, and are the basis of Rafter's diagrams and expo- 
nential equations. While such methods are an improvement on per- 
centage expressions, they fail to take into account many factors which 
must greatly affect the flow of streams. 

LITERATURE 

River Discharge, J. C. Hoyt and N. C. Grover, John -Wiley & Son, N. Y., 1916. 
Hydrographic Manual, E. C. Murphy, J. C. Hoyt and G. B. Hollister, U. S. G. S. 

Water Supply Paper 94, 1904. 
Accuracy of Stream Measurement, E. C. Murphy, U. S. G. S. Water Supply 

Paper 95, 1904. 
American Practice in Stream Measurement, F. C. Shenehon, Eng. News, 

Vol. 52, p. 365, 1904. 
Method of Computing Daily and Monthly Discharge of Streams with Sandy 

Changeable Beds, E. C. Murphy, Eng. News, Vol. 51, p. 379, 1904. 
Determination of Stream Flow during the Frozen Season, H. K. Barrows and 

R. E. Horton, U. S. G. S. Water Supply Paper 187, 1907. 
Effects of Ice on Stream Flow, W. G. Hoyt, U. S. G. S. Water Supply Paper 337, 

1913. 
Equipment for Current Meter Gaging Stations, G. J. Lyon, U. S. G. S. Water 

Supply Paper 371, 1915. 
Accuracy of Stream Flow Data, N. C. Grover and J. C. Hoyt, U. S. G. S. Water 

Supply Paper 400, 1916. 
Stream Gaging Stations and Publications relating to Water Resources 1S85- 

1913. U. S. G. S. Water Supply Paper 340, 1914. 



CHAPTER XVIII 

ESTIMATING RUNOFF 

231. Rational Methods of Estimating Runoff, — Various methods 
of estimating runoff by percentage of rainfall, by experimental equations 
and by curves or lines drawn to fit the observed seasonal or annual 
rainfall-runoff relations, as nearly as practicable, have been discussed 
in Chapter XVII. In these cases rainfall was the only factor used as 
a basis for such estimates. The factors which must be considered in 
any rational method of computing runoff are : 

1. Rainfall and its distribution throughout the year. 

2. Losses from evaporation, transpiration and deep seepage. 

3. Temperatures, humidities and wind velocities. 

4. Topography, surface condition of soil and vegetation. 

5. Storage conditions (surface and sub-surface). 

To approximate the actual annual runoff conditions it clearly is neces- 
sary to take into account at least the physical conditions on the drainage 
area that most greatly influence runoff ; and if the attempt is to be made 
to calculate average monthly runoff it will also be necessary to consider 
those conditions which cause the lag in rainfall effects discussed in Sec. 
214. 

In 1889 Thomas Russell 1 offered the following formulas for the run- 
off of the Ohio and Upper Mississippi Valleys. His formula for the 
Ohio River was as follows : 

r , (I ,. (1) D = 0.600 + 0.95 R — 0.90 R (0.975 e — 0.421 e2 + .066 e~) 
and for the Upper Mississippi 

(2) D = 0.50 + 0.93 R — 0.88 R (1131 e — 0.383 e«) 

In these formulas 

D = Runoff in cubic miles 
R — Rainfall in cubic miles 
e = Quantity of water necessary to saturate the air at any time 

There is in these formulas a recognition of the fact that each stream 
is subject to a separate law and that certain atmospheric conditions will 
modify the rainfall-runoff relations. These formulas are found to 
agree but roughly with the observed stream flows. 



1 Rainfall and River Outflow in the Mississippi Valley, by Thomas Russell, 
Ann. Rept, Chief Signal Officer for the year 1889, Part 1, Appendix 14. 



5 1 Estimating Runoff. 

232. Vermuele's Method. — C. C. Vermuele 2 has derived various 
formulas for calculating the annual and monthly runoff of streams, 
based on certain relations between retention and runoff which he claims 
to have discovered. His general formulas for annual runoff are : 

(1) F = R — E 

(2) B= (15.50 + 0.16 R) (0.05 T — 1.48) 

and for the Sudbury. Croton and Passaic Rivers 

(3) E = 15.50 + 0.16 R 
In which 

F = Annual Runoff in inches 
R = Annual Rainfall in inches 
E = Annual Retention in inches 
T = Mean annual temperature 

Mr. Vermuele's formulas for the monthly flow of the Sudbury, 

Croton and Passaic Rivers are : 

(e = Monthly Retention r = Monthly Rainfall) 

December e = 0.42 + O.lOr 

January e = 0.27 + O.lOr 

February e = 0.30 + O.lOr 

March e = 0.48 + O.lOr 

April e = 0.87 + O.lOr 

May e = 1.87 + 0.20r 

June e = 2.50 + 0.25r 

July e= 3.00 + 0.30r 

August e = 2.62 + 0.25r 

September e == 1.63 + 0.20r 

October e = 0.88 + 0.12r 

November e = 0.66 + O.lOr 

Year E = 15.50 + 0.16R 

The values for monthly retention (e) for other streams are obtained 
by multiplying the results obtained from the formulas for each month 
by the factor (0.05T — 1.48) 

Mr. Vermuele's formulas for depletion are : 

(4) d2 = di + e + f — r 

f r — e 

(5) d = 1- di 

2 2 

in which 

di = Depletion at the end of the previous month 

d2 = Depletion at the end of the month under consideration 

d = Average depletion 

e = Monthly retention 

r = Monthly rainfall 

f = Monthly runoff 

- Water Supply, by C. C. Vermuele, Vol. 3, Geol. Survey of New Jersey, 1894. 



Vermuele's Method. 



511 



With all quantities in Equation 5 known by calculation or by obser- 
vation except f, f can be calculated from the curves shown in Fig. 289, 
or from similar curves for any other streams. Later Mr. Vermuele 3 
modified his formula for annual retention as follows : 

(6) E = (11 + 0.29R) M 

in which E and R have the same significance as in Equations 1, 2 and 3, 
and 

M is a factor depending on the mean .temperature of the atmosphere 
as follows : 

TABLE 49 
Shoiving Values of M Corresponding to Mean Annual Temperature 



Mean Annual 
Temperature 

40 


Factor 

M 

0.77 


Mean Annual 
Temperature 

51 


Factor 
M 

1.10 


41 


0.79 

0.82 

0.85 


52 


1.14 


42 


53 


1.18 


43 


54 , 


1.22 


44 


0.88 

0.91 


55 


1.26 


45 


56 


1.30 


46 


0.94 


57 


1.34 


47 


0.97 


58 

59 . . 


. 1.39 


48 


1.00 


. 1.43 


49 


1.03 

1.07 


60 


1.47 


50 


61 


1.51 



On page 149 of the report on forests 3 , Mr. Vermuele compares ob- 
served and computed annual retention, and while in many of the results 
the agreement is quite close, some of the maximum differences shown 
are as follows : 

TABLE 50 

Table Shoiving Maximum Differences Between Observed and Calculated Mean 

Animal Retentions by Vermuele Formula 



River 


Observed 


Retention 
Calculated 


Difference 


Inches 


Inches 


Inches 


Percent 


Potomac 


24.8 
27.2 
20.5 
21.3 
24.4 
24.2 
25.0 


28.9 
20.6 
24.0 
28.2 
28.3 
28.2 
19.8 
24.5 
17.4 


—4.1 
+6.6 
—3.5 
—6.9 
—3.9 
—4.1 
+ 5.2 
+4.8 
—2.7 


—17 


Genesee 


+24 


Pequest 

Tohickon 

Desplaines 


—17 

—32 
—16 
—17 

+21 




29.3 

14.7 


+17 
—18 



:! Ann. Rept. State Geologist of New Jersey on Forests, 1899. 



512 



Estimating Runoff. 



This table indicates the necessity of great care in the use of any such 
formulas for the calculation of even mean annual flow. The danger 
of attempting to adapt such formulas to seasonal flows is much greater. 
It is shown by Rafter (Fig. 297) that retention has no fixed relations 



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5?>5> 5 5 5 5 5 5 5 Sf 5 5 5 5 $ 83 5 5 $ 5 55 5 5 5 5 ? 5 5 5 ^ 5 5 s> 5 § 5 5 * ? 5 5 5 5 5 5 5 5 5 Si 5 5 5 

Fig. 297. — Diagrams of Retention and Temperature for Two Streams in East- 
ern United States. After G. W. Rafter. 

to mean temperatures, at least when considered as an independent factor, 
and that therefore the fundamental bases of Mr. Vermuele's formula 
are not correct or safely applicable to general calculations of this nature. 
233. Justin's Method. — J. D. Justin 4 has suggested an expression for 
annual runoff in the eastern United States as follows : 

R2 

Fr= 0.934 SOiss — 



in which 

F = Annual runoff in inches 

R = Annual rainfall in inches 

S = Slope of drainage area found by dividing the maximum dif- 
ference in elevation on the drainage area by the square 
root of the drainage area 

T =Temperature of the drainage area in degrees Fahrenheit 

Mr. Justin suggests the use of this formula to determine monthly 
runoffs for the calculation of data for mass curves. Such curves he 
regards as inaccurate as to individual months but states that such in- 



* Derivation of Runoff from Rainfall Data, by J. D. Justin, Trans. Am. Soc. 
C. E., Vol. 77, p. 346. 



Justin's Method. 513 

accuracies will" not affect the conclusions as to the necessary size of the 
reservoir for a given draft. He believes that the formula is "applicable 
to the Eastern United States and in general should give results within 
10% of the true runoff." His tables, while agreeing more closely with 
the mean annual runoff of many streams, show a maximum difference 
in that calculated from the mean annual flow on the Passaic River of 
4.6 inches or over 18 per cent, and would evidently vary still more from 
annual values. 

Mr. Justin makes no attempt to determine the actual monthly distri- 
bution of runoff in more than a most approximate way, and the curves 
representing the expression cannot and do not agree with the observed 
annual rainfall-runoff relations any closer than the experimental equa- 
tions of Rafter. He takes into account temperature and slope but neg- 
lects the ground flow conditions which make it impossible to approxi- 
mate closely the seasonal variations in flow. 

234. Meyer Method. — Professor A. F. Meyer 5 has presented a 
method of "computing runoff from rainfall and other physical data." 
In his investigations of northern states, Professor Meyer compares a 
rainfall year for a 12-month period beginning November 1, with a 
corresponding runoff year beginning on the following March 1. 

This method is quite involved and depends upon such a complete 
knowledge of the physical conditions on the drainage area that ap- 
parently it is applicable only when more knowledge is possessed than is 
common in the majority of such problems. Its author has, however, 
applied it with considerable success to areas where no such detailed 
knowledge seems possible, such for example as the Ohio River above 
Wheeling, with 23,820 square miles of drainage area, and the Colorado 
River at Austin, Texas, with 37,000 square miles of drainage area. 

The method is made applicable only by the acceptance of certain 
transpiration, evaporation, soil storage, seepage and surface flow curves 
which in turn depend upon a detailed knowledge of the peculiarities of 
flow that have taken place on the drainage area. The transpiration and 
evaporation curves are based on a consideration of the theoretical 
factors involved and of various experimental researches and were 
modified and revised until they gave the best results when actu- 
ally applied in estimating stream flow. The curves for soil storage, sur- 
face flow and seepage flow for the calculations of the monthly runoff 

s Computing Runoff from Rainfall and other Physical Data, by A. F. Meyer, 
Trans. Am. Soc. C. B., Vol. 79, p. 1056, 1915; also Hydrology, by A. F. Meyer, 
John Wiley and Son. 1917. 

Hydrology — 33 



5 1 4 Estimating Runoff. 

of the Root River, in which calculations Professor Meyer's methods are 
most completely examplified, were derived by their author "not from 
any group of data but on a process of logical reasoning, experience, ob- 
servation, and all the facts bearing on the subject which he could com- 
mand." These curves cannot be reproduced from any data or on any 
scientific basis. To use this method it is essential to accept these 
graphical empirical expressions for various constants and modify them 
on the lines suggested by the author and by the actual runoff relations 
found to exist on any drainage area to which they are applied, and this 
cannot safely be done except by or under the direction of an experienced 
hydrologist. 

This method was presented as furnishing a skeleton of basic princi- 
ples, and steps in the computation of runoff to which any degree of re- 
finement may be applied to the computation by taking into account 
variations from the normal meteorological conditions on a given drain- 
age area. The author states that his method should be used "princi- 
pally for the purpose of analyzing, supplementing and extending ob- 
served stream flow records so as to make these records a better basis for 
works of improvement into which runoff enters as a factor." This 
method presents a distinct advance in the attempt to analyze runoff 
phenomena inasmuch as all of the principal factors that influence the 
flow of streams are considered. The disadvantage of this method lies 
in the necessity of accepting, temporarily at least, certain empirical 
variable coefficients to be taken from curves which cannot be either 
verified or corrected except at great labor and after many trials. Its 
danger lies in their acceptance without verification and their use under 
conditions to which they are not applicable. 

235. Basis of all Methods of Stream Flow ^Analysis. — In general 
it will be seen that all of the methods which have been suggested or can 
be devised for analyzing runoff are necessarily the result of correlating 
observed effects (runoff) and more or less complete data of physical 
causes (rainfall, evaporation, transpiration, temperature, etc.). The 
problem is : Given a long detailed record of stream flow together with 
more or less detailed knowledge of physical conditions, to determine a 
rational method of applying the known data so that the calculated values 
of runoff will agree with the observed flow. The object of such 
methods are : 

rst. To extend available observations and thus to determine the prob- 
able effects of more extreme conditions of rainfall, drought and other 
factors on stream flow. 



Basis of Stream Flow Analysis. 5 1 5 

2d. To enable the engineer to approximate the runoff which will ob- 
tain from any drainage area where only limited stream flow data are 
available. 

Such studies intelligently made possess a great value in familiarizing 
the engineer with the influence of the various factors on the resulting 
stream flow, and in extending his knowledge of the stream flow which 
may have been experienced under extreme conditions which may have 
occurred but for which no records of flow are available. They are also 
of importance in the determination of the necessary information to be 
sought in the investigation of new areas, but they do not furnish a 
method which can be applied to the solution of such problems for new 
areas, and their use for such calculations by those who have not made a 
profound study of the entire subject, is liable to give the results of such 
calculations a weight to which they are not entitled. 

At the present time there seems to be no rational method that can 
readily be applied to the accurate estimate of the seasonal distribution 
of runoff. In the writer's opinion, when long term records are avail- 
able comparative hydrographs of adjacent streams should be used and 
corrected for differences in physical conditions and by at least short 
time observations on the stream in question. Investigations along the 
lines suggested by Professor Meyer should also be undertaken to con- 
firm or correct the opinions so derived. The danger in the use of com- 
parative hydrographs is evident for the great differences which often 
occur in the flow of adjacent streams have already been emphasized. 
Professor Meyer expresses the opinion that comparative hydrographs 
are of little value for supplementing stream flow data unless the char- 
acteristics of two drainage areas are identical. While this is true it is 
also true that calculations for any stream where runoff data are n'ot 
available cannot be made with any greater degree of accuracy from the 
characteristics of any other stream unless it has identical characteristics 
which in turn cannot be determined without extended observations and 
actual stream flow data. 

The hydrograph is a correct expression of the detailed runoff of a 
stream, resulting from all the varying physical conditions which have 
occurred on the drainage area above the gaging station previous to the 
time which it represents. It will express the flow of any other stream 
only when correctly modified for the different physical conditions which 
have obtained on the comparative area during the corresponding period. 
The effects of such differences can be only approximately determined, 
and the comparison is always correspondingly inexact. 



5 1 6 Estimating Runoff. 

236. Runoff Problems. — In estimating runoff the method employed 
must necessarily vary with the purposes for which the information is to 
be used. In general the information sought will involve the total run- 
off available under certain conditions of storage and distribution. 

It is evident from a study of the hydrographs previously discussed 
that there are but few cases in which all of the runoff of a stream can 
be utilized to advantage under all conditions of flow. The works for 
the control and utilization of a stream must be built at considerable cost 
and their size and capacity should be limited so that the returns from 
the flow conserved will result in an amount adequate to meet with a safe 
margin, fixed charges, operating costs and maintenance. It is in gen- 
eral impracticable therefore to develop works of this kind so that they 
will be utilized to their capacity only once in a long term of years, for 
the cost will be too great for the benefit received. 

In some cases where works are comparatively simple and inexpensive 
and the value of the water conserved is very great, as in the case of 
public water supplies for large cities, works of sufficient capacity to 
utilize the total flows of the lowest three to five years may be practicable. 
In other cases, the practicability may be limited to the total flow of the 
lowest year. In still other cases the flow which can be made available 
for the average six to eight months may be the limiting requirement ; 
while in still other cases the flow which can be made available for the 
month or week of lowest flow may control. 

Every case is a special problem which may vary within wide limits 
and must be solved in some practicable manner, that will give dependable 
results commensurate with the risk to life, health and property involved. 
The problems involved may include conditions : 

1st. When sufficient runoff data are available, and the information 
sought is the amount of water which can be utilized with more or less 
storage. 

2d. When no runoff data or only limited data are available, and when 
the probable runoff must be estimated by comparison with the flow of 
other streams or calculated from data derived from the flow of other 
streams. 

In either case the condition may include problems : 

A. Where storage is sufficient to equalize the supply over a series of 
dry years or at least over a series of dry months. 

B. Where storage is sufficient to improve the average flow of one or 
two low months. 



Runoff Problems. 517 

C. Where storage is sufficient to improve the flow of the days of low 
runoff. 

D. Where storage is only sufficient to impound the low or average 
day's flow and make it all available during a portion of the day during 
which it is to be utilized. 

In many problems of runoff the amount of storage available is 
a very important consideration. If storage is available sufficient to 
equalize the flow of a stream for a series of years, a knowledge of the 
variations in the annual runoff may be of primary importance, and the 
distribution of runoff during the year may be secondary. If the storage 
is sufficient to equalize the flow of the lowest year, or even of the one 
or two lowest months, then the monthly flow may be of primary im- 
portance and the distribution of flow through the month may be of little 
importance. In cases of limited storage, where equalization can be 
accomplished only for a few weeks or a few days, a knowledge of the 
daily distribution of flow becomes essential. 

Storage then is frequently an important factor, and the problem may 
be to determine : 

a. What storage is necessary to accomplish a certain equalization of 
flow ; or 

b. What equalization of flow can be accomplished by a certain avail- 
able storage. 

ESTIMATING AVAILABLE FLOW FROM KNOWN RUNOFF 

237. Runoff Problems with Large Storage (Flow Known). — 

Rippl's graphical method of storage computation is of much value where 
it is desirable to utilize the average flow of a series of dry years or 
months by storage. This method consists in representing the net yield 
of a stream graphically by a mass diagram for the entire period for 
which observations are available or for such special dry periods as will 
control the extent of the project. 

From a study of mass diagrams of the net available runoff may be 
determined : 

1. The quantity of storage necessary for its utilization ; or 

2. The net flow that can be utilized with a known amount of storage. 
To use this method of investigation the observed or estimated flow 

of the stream for each month is reduced by the loss due to evaporation, 
seepage, etc. The remainder represents the net quantity of water 
available. The summation of these monthly balances, added one to the 
other consecutively are then platted in a curve in which the abscissa of 



518 



Estimating Runoff. 



each point represents the total time from the beginning of the period ; 
and the ordinate, the total quantity of water available during the same 
interval. The scale may represent inches on the drainage area, cubic 
feet, acre feet, or such other unit as may be desired. Such a curve is 
represented in Fig. 298, by the irregular curve A-B-C-D-E-F. 



600,000 



JOO.COO 




Fig. 298.- 



Monthj. 
-Diagram of Rippl Method of Storage Calculations. 



The inclination of the curve at any point indicates the rate of the net 
flow at that particular time. When the curve is parallel to the horizon- 
tal axis, the flow at that time will just balance the losses caused by 
evaporation, seepage, etc. A negative inclination of the supply line 
shows that a loss from the reservoir is taking place. 

In a similar manner the curve of consumption can be platted. For 
most purposes this can be considered a straight line as the variation in 
the use of water from season to season is a refinement not usually war- 
ranted, unless the uses to which it is to be put at various times of the 
year are well established. In Fig. 298, a series of straight lines of con- 
sumption are drawn, representing the use of water at rates of 100 to 
700 acre feet per day. These rates correspond essentially to rates of 
from 50 to 350 cubic feet per second. 

The ordinate between the supply and any demand line represents the 



Runoff with Large Storage. 5 1 9 

total surplus from the beginning of the period considered, and when 
the inclination of the supply line is less than that of the demand line, 
the yield of the drainage area is less than the demand and a reservoir 
is necessary. 

The deficiency occurring during dry periods is found by drawing lines 
parallel to the demand line, or lines, and tangent to the curve at the 
various summits of the supply curve, as at B. 

The maximum deficiency in the supply, and the necessary capacity of 
the reservoir to maintain the demand during the period, is shown by 
the maximum ordinate drawn from the tangent to the curve itself. The 
period during which the reservoir would be drawn below the high water 
line is represented by the horizontal distance between the tangent point 
and the first point of intersection of the curve. If the tangent from 
any summit parallel to any demand line fails to intersect the curve, it 
indicates that, during that period, the supply is inadequate for the de- 
mand. To insure a full reservoir it is necessary that a parallel tangent 
drawn backward from the low points on the supply curve shall intersect 
the curve at some point below. For example, the line B-7, representing 
a daily consumption of 700 acre feet, does not again intersect the curve 
and is therefore (within the period represented by the diagram) beyond 
the capacity of the stream. The line B-6 intersects the curve at E and 
is the limit of the stream capacity. Such a consumption will be pro- 
vided by a storage of about 115,000 acre feet as represented by the 
length of the line 6-D, and such a reservoir will be below the flow line 
for about twenty-two months during the dry period illustrated in this 
diagram. That this reservoir will fill is shown by the intersection of 
the lower tangent D-A with the curve near A. The conditions neces- 
sary to maintain rates of 500, 400, and 300 second feet are shown re- 
spectively by the tangents B-5, B-4, and B-3, and the verticals 5-D, 
4-C and 3-C. 

If the amount of storage is known, and it is desired to ascertain the 
maximum demand that can be satisfied by such fixed capacity, the rate 
is determined by drawing various tangent lines from the summits, hav- 
ing the maximum ordinates equal to the fixed storage. 

Mass curves showing the effects of evaporation resulting from 
various reservoir areas on the available flow of Tohickon Creek are 
shown in Fig. 89, page 153. The details of the computations on which 
these curves are based are given in another volume. 6 



e Water Power Engineering, by Daniel W. Mead, McGraw-Hill Book Co., 
1915, 2d Ed., p. 179. 



520 Estimating Runoff. 

238. Runoff Problems with Moderate Storage (Flow Known). — 

When the storage available is moderate in comparison with the runoff 
available, a method of analysis suggested by Mr. S. B. Hill may be used 
to advantage. This method is illustrated by an analysis made of the 
probable available flow of a southern river. Fig. 299 shows the mean 
monthly flow of the river in question for the years 1893 to 1906 in- 
clusive. As the higher monthly flows can not be made available the 
diagrams of flows above 1755 cubic feet per second are not shown. The 
available storage was 51,000 acre feet or 2,221,560,000 cubic feet, 
which is equivalent to a flow of 857 second feet for thirty days. 

The maximum daily continuous flow (A. A. Fig. 299) is determined 
by the effect of the driest year (viz. 1904) on the storage. The effect 
of the dry periods on the storage is shown by the indentation into the 
lower or storage line of the diagram. In the year 1904 the reservoir 
capacity Avould have been just exhausted in order to maintain the maxi- 
mum flows during the low months of September, October and Novem- 
ber of that year. The amount of available continuous flow (i. e. the 
position of the line A- A) is determined by equalizing the deficiency in 
flow during the dry months with the total reservoir capacity. 

It is important in the study of storage to see that in the intervening 
periods of excessive flow, such flows are sufficient to supply the defi- 
ciency occasioned by previous demands on the reservoir, otherwise the 
dry period must be considered in its relation to subsequent periods in 
determining the available continuous power (see Fig. 299, 1897 and 
1898). 

The daily flow of this river for the year 1904, is shown by the hydro- 
graph. Fig. 301, from which it will be seen that without storage, the 
available flow of this stream would be limited to a minimum of 268 acre 
feet per day. 

In order to maintain a continuous supply greater than that due to 
the minimum flow of the stream with storage, some source of auxiliary 
supply such as wells for water supply or irrigation problems, or some 
source of auxiliary power such as steam for power developments, 
must be available. If it is not desired to utilize the flow of the stream 
to a greater capacity than indicated in Fig. 299 or by a capacity of 1,372 
acre feet per day, making the total acre feet available 1,640 (represented 
by line B-B, Fig. 300), an auxiliary supply or auxiliary power to the 
extent represented by the double cross hatched areas on this diagram, 
would be needed. As at all other times water would be available, the 
addition of steam auxiliary power apparently would be warranted to 



Runoff with Moderate Storage. 




£> <i Ci 'i ^ <J> 
<M "o <o ^ ^F K 

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cv» <o oq c; 

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puojag- -/ad jaaj o/qny 



522 



Estimating Runoff. 



supply the deficiency for a power development ; and if the supply is to 
be used for irrigation purposes, a series of wells to be pumped by aux- 
iliary power at times of deficiency might be warranted. 

239. Runoff Problems with Limited Storage (Flow Known). — 
In the low head water power projects and in similar supply projects for 
other purposes where the storage is small in relation to the total amount 





Jan 


Feb. 




Mar 


Apr 


May 


June 


July 


Aug. 




■Sept. 


Oct. 


Nov 


Dec. w 


X5 












1904- 








































































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Fig.' 301. — Hydrograph of a Southern River. 

of streamflow, it frequently becomes desirable to analyze the probable 
available flow when the storage is fully utilized or to calculate the 
amount of storage which will be necessary to accomplish certain re- 
sults. 

Under these circumstances it becomes desirable to prepare hydro- 
graphs of the daily flow of the stream and to analyze the flow from 
month to month and from week to week in order to determine what the 
results would have been if such storage conditions had obtained in the 
past so that the future may be predicted with more or less certainty. 

In 1917 such an analysis was made of the flow of the Colorado River 
at Austin, Texas, in order to determine the financial bearing of certain 
proposed betterments in the dam and power station at that place. 7 In 
this case almost 20 years of streamflow records were available and daily 
hydrographs were platted for each year. Each hydrograph included 
only so much of the flow as might be practically utilized in order that 
the scale would be sufficiently large to calculate graphically the effect of 
pondage and the auxiliary power needed to maintain a constant output 



Report on the Austin Dam, by Daniel W. Mead, City of Austin, 1917. 



Runoff with Limited Storage. 



523 



of 3,300 horse power. Fig. 302 shows three of these hydrographs for 
conditions as follows : 

A. For the year of maximum runoff, 1900. 

B. For a year of mean runoff, 1904. 

C. For the year of minimum runoff, 19 10. 

The results of the investigations for these years and the means for the 
entire period for which data were available are shown in Table 51 and 
also graphically in Fig. 303. 

TABLE 51 

Showing Amount of Hydraulic Power which Could have been Delivered by the 
Austin Hydraulic Power Plant with a 60-Foot Head and the Normal Flow 
of the Stream; also the Amount of Auxilary Power Necessary to Maintain 
3,300 Continuous Horse Power During Certain Years and for the Mean of 
the Period from 1898 to 1917, Inclusive. 

In Thousands of Horsepower Hours 





1900 


1904 


1910 


Mean 
1898 to 1917 


Period 


Hydrau- 
lic 


Steam 


Hydrau- 

v lie 


Steam 


Hydrau- 
lic 


Steam 


Flydraii- 
lic 


Steam 


February 

May 

July 

September . . . 

October 

November .... 
December .... 


2,480 
2,240 
2,480 
2,400 
2,480 
2,400 
2,480 
2,480 
2,400 
2,480 
2,400 
2,480 




















1,087 
1,050 
1,126 
1,432 
2,480 
2,400 
2,440 
2,240 
2,355 
2,480 
1,260 
1,060 


1,393 

1,270 

1,354 

968 





40 

240 

45 



1,140 

1,420 


1,013 

883 

973 

2,320 

2,267 

776 

742 

736 

1,288 

1,070 

527 

533 


1.407 
1,357 
1,507 
80 
213 
1,624 
1,738 
1,744 
1,112 
1,410 
1,873 
1,947 


1,397 
1,304 
1,520 
1,831 
2,237 
2,116 
2,073 
1,805 
1,847 
1,857 
1,567 
1,584 


1,083 
952 
960 
569 
143 
284 
407 
675 
553 
623 
832 
896 


Percentage . . . 


29,200 
100 






21,410 


7,870 


13,123 


16,072 


21,300 


7,920 


67.7 


32.3 


44.9 


55.1 


72.9 


27.1 



While this is a special application to the study of a water power pro- 
ject with steam auxiliary, it is evident that the method used may also 
be applied to water power or water supply projects where a secondary 
source with comparatively large pondage may be used as an auxiliary 



supply. 



ESTIMATING AVAILABLE FLOW FROM COMPARATIVE HYDROGRAPHS 

240. Comparative Hydrographs with Large Storage (Flow 
Unknown). — The use of comparative hydrographs for estimating the 



524 



Estimating Runoff. 




Jan Feb. Mar Apr May June July Aug Sept Oct Nov. Dec. 

mmmm mmm Y//////////A 

Seepage.Fvaporation and Pondage Auxiliary Steam 

Flow of Barton Spring 

Fig. 302. — Power Hydrographs of the Colorado River. at Austin, Texas (see 

page 523). 















?//, 


w 


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WMWM 


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c 




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— / 


lean 


Hy< 


Jrat. 


'lie ? 


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O 




20 


\ 


40 




% 

<0 


60 


SO 








\ s. >s \ 



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Fig. 303. — Proportion of Yearly Auxiliary Power Necessary to Maintain 3,300 
Continuous Horse Power on Colorado River at Austin. (See page 523.) 



Comparative Hydrographs. 



525 



flow of a stream where little or no runoff data are available is consider- 
ably simplified when large storage is practicable. During 1918 it became 
desirable to determine the probable amount of runoff of the Ashtabula 
River near Ashtabula, Ohio, that could be utilized for power purposes by 
the construction of certain reservoirs on the drainage area. There 
were no stream flow measurements available from the drainage area, 
hence it became necessary to estimate the probable runoff from the com- 
parative runoff of other streams. 

r. Comparative Drainage Areas. There were available for com- 
parative purposes runoff measurements on nearby streams as follows : 



Steam 


Location 


Area 
Sq. 

Miles 


Data Available 


Shenango River. . 
Cussewago Creek. 
Shenango River. . 
Shenango River. . 

French Creek 

French Creek 


Sharon, Pa 

Near Meadville, Pa 

Greenville, Pa 


610 

90 

152 

107 


1-1-1910 to 1-1-1918 
6-1-1910 to 1-1-1918 
2-1-1912 to 1-1-1918 
1-1-1914 to 1-1-1918 
5-1-1910 to 1-1-1918 
5-1-1910 to 1-1-1918 



The records of the last two stations were defective as the rating 
curves were not well defined. The published data for French Creek 
at Kimmeytown indicated annual runoff almost equal to the annual 
rainfall, thus showing their unreliability. These two streams were also 
at a considerably greater distance from the Ashtabula River than the 
first four, so that the data from the first four streams were used in the 
computations. 

Fig. 304 is a map of the region adjacent to Ashtabula, showing the 
relative location of the Ashtabula River and of the four drainage areas 
used as a basis for comparison, and also the location of the nearest sta- 
tions where rainfall records were available, viz., at Erie, Saegerstown 
and Greenville, Pa., and at Warren, Hillhouse and Cleveland, Ohio. 

Without considering the area of the reservoirs, the drainage area 
above the lower proposed reservoir dam on the Ashtabula River was 
116 square miles. For safety this was estimated at 100 square miles, 
thus making an allowance for safety of i6°/o on runoff calculations. 

2. Reservoir Capacity. In considering the development proposed, 
it seemed to be practicable to construct reservoirs having a total usable 
capacity of 1,589,500,000 cubic feet, and the estimates were made on 
this basis. 



526 



Estimating Runoff. 



3. Mass Curves of Runoff. Mass curves of each stream (Fig. 305) 
showing the accumulated sum of the monthly runoffs in cubic feet per 
second per square mile were first platted, and the rates at which the 
water could be used were then determined. The rate lines are the in- 
clined lines shown on the diagrams and begin in each mass curve at 
various dates when the reservoir can be considered as filled. The slope 
of these rate curves is determined by two requirements : 

1. The capacity of the reservoir. 

2. The requirement that the reservoir must be full at the close of the 
period. 




'eteger'sfown 



Fig. 304. — Region of the Ashtabula River and Comparative Drainage Areas. 

(See page 525.) 

The capacity of the reservoir is indicated on the drawing by the height 
of the vertical lines drawn near the center of the rate lines and near the 
middle of the periods of deficient stream flow. The vertical lines which 
occasionally appear at the end of one rate line and at the beginning of 
another show the amount of water which would reasonably have been 
wasted for lack of greater reservoir capacity. The rate lines at the 
end of December, 19 17, are drawn so as to leave the reservoirs at that 
date partially filled to provide for partial deficiency at the beginning of 
1 9 18, although the runoff records show that the streamflow during the 



Comparative Hydrographs. 



527 



first three months will probably fill the reservoir, in addition to supply- 
ing water for a fair rate of use. 

4. Estimates of Usable runoff. — The results of the computations for 
mean monthly runoff are shown on the mass curves and are summarized 
in the following table : 

TABLE 52 

Regulated Mean Annual Flow of the Ashtabula River in Cubic Feet Per Second 
Per Square Mile (with Storage) Based on the Actual (Regulated) Floio 
of Comparative Streams. 



River Above 


Shenango 
Sharon Pa. 


Shenango 
Turnersville, Pa. 


Little Shenango 
Greenville, Pa. 


Cussewago 
Meadville, Pa. 




610 sq. mi. 

1.26 
1.35 
1.62 
1.25 
1.06 
.99 
1.06 
1.10 


152 sq. mi. 


107 sq. mi. 


90 sq. mi. 


Year 

1910 




1911 






1.75 


1912 . 


1.58 
1.39 
1.22 
1.24 
1.17 
1.39 




1.64 


1913 




1.33 


1914 


1.18 
l.o3 
1.24 
1.18 


1.21 


1915 


1.19 


1916 

1917 


1.20 
1.20 






Mean 


1.21 


1.33 


1.23 


1.36 







Mean of all records 1.285 

5. Hydrographs. — The hydrographs (Fig. 306) were also made on 
the basis of the average monthly runoff in cubic feet per second per 
square mile. The use, storage and waste of water is also indicated by 
the shaded areas. This shows in a different way how the flow could be 
utilized. This form of diagram if drawn to a large scale on cross sec- 
tion paper may also be used in calculating the available stream flow by 
making the water used during the dry period equal the excess runoff. 
This method is ordinarily less accurate and does not so clearly indicate 
the limiting effect of storage. The average of all the records of mean 
annual flow for these streams is 1.28 cubic feet per second per square 
mile. 

6. Geological Conditions. — In general the drainage areas of all the 
streams in question are covered by drift varying from 25 to 75 feet in 
depth. The underlying indurated formations are not known in detail, 
but the entire Ashtabula River drainage area lies within the area of 
Devonian shales, while the other stream areas lie almost entirely within 



528 



Estimating Runoff. 



an area of carboniferous limestones, sandstones, conglomerates and 
shales. Normally it would be expected therefore that the flow of the 
Ashtabula River would be somewhat greater than that of the other 
streams for the character of the underlying deposits of the four com- 




/9/0 1911 /9/2 /9/3 /9/4 /9/5 (9/6 /9I7 

Fig. 305. — Mass Curves of Runoff of Various Streams near Ashtabula, Ohio. 

(See page 526.) 

parative streams would probably lead to some losses from deep seepage 
which would not occur on the Ashtabula drainage area. 

7. Rainfall. — To determine the distribution of the annual rainfall 
for the eight years for which runoff data were available, maps were 
drawn (Fig. 307) on which were platted isohyetal lines, for the water 



Comparative Hydrographs. 



529 



/9/3 



/S/6 



~ 



'. >'>''.'7? 



T 



V//// 



m^ 



Re /a t/ve Discharge, L i / //e Shenango River at Greenv///e, Pa. 




Re/a /ive Discharge, Shenango River at Turner ■i/i/Ze, Pa. 




Re/a five Discharge, Shenango R/ver at Sharon, Pa. 




Re /a// ye Discharge, Cussewago Creek near r/eadvi/Ze, Pa. 



Fig. 306. — Comparative Hydrographs of Streams near Ashtabula^ Ohio. (See 

page 527.) 



Hydrology — 34 



530 



Estimating Runoff. 




A. indicates Drainage Area of Ashtabu/a PiVer near Ashfabu/o. Oh/o. 
C- indicates Drainage Area of Litt/e Shenango Piver af <jreenvif/e,Pa 
M. indicates Drainage Area of Cossetvago Creek near rleadfri/e , Pa 

T. indicates Drainage Area of Shenango Pir-er af Tornervi//e , Pa 

T. G.S. •• Drainage Area of Shenango Piyer af Shanpn, Pa. 

Fig. 307. — Distribution of Annual Rainfall on Drainage Areas near Ashtabula, 

Ohio (see page 528). 



Comparative Hydrographs. 



53 



year November i to November i for each year, and from these maps 
the approximate annual rainfall on each drainage area was estimated. 
These data together with the mean annual runoff of each stream for 
each year of record are shown in Table 53. 



TABLE 53 

Annual Rainfall and Annual Runoff in Inches on Various Drainage Areas 
Near the Ashtabula River. 



Year 


Shenango 
Sharon 


Turnersville 


Little Shenango 
Greenville 


Cussewago 
Meadviile 




Rain 


Runoff 


Rain 


Runoff 


Rain 


Runoff 


Rain 


: Runoff 


1910 


37.8 
48.5 
47.5 
43.8 
40.4 
40.6 
37.8 
42.6 


15.43 
21.55 
19.37 
20.68 
15.37 
33.11 
14.59 
18.03 












1911 








45.5 
43.5 
46.5 
39.3 
42.0 
42.5 
48.4 


27.48 


1912 










21.40 


1913 

1914 . . ." 

1915 

1916 

1917 


45.5 
40.6 
39.8 
39.8 
45.5 


23.99 
21.19 
18.33 
18.61 
21.69 


41.4 
41.5 

38.8 
44.5 


18.76 
18.65 
17.01 
21.18 


22.88 
16.50 
19.07 
17.81 
20.37 




42.10 


17.37 


42.24 


20.74 


41.55 


18.65 


43.96 


20.79 



Mean of table of annual runoff == 19.29 inches = 1.40 sec. ft. per sq. mile 

A diagram (Fig. 308) was also prepared showing the mean annual 
rainfall for the period of record. This diagram shows that at Saegers- 
town, Pa., and at Hillhouse and Cleveland, Ohio, the mean annual rain- 
fall for the seven years was less than the mean annual rainfall for the 
period of record, while at Erie and Greenville, Pa., and at Warren, Ohio, 
the mean annual rainfall for the seven years was greater than the mean 
annual rainfall for the period of record. 

A mean annual rainfall map (Fig. 309) was also drawn from the 
best available long-term data to show the mean annual rainfall on all of 
these drainage areas. From this map it will be seen that the mean 
annual rainfall on the Ashtabula River drainage area has been approx- 
imately 40.5 inches. A comparison of the mean annual rainfalls shown 
on this map, with the mean annual rainfalls for the periods of runoff 
records, given in Table 53, will show that in general the long time an- 
nual rainfall means are less than the means for the periods for which 
runoff data are available (except on the Cussewago Creek drainage 



532 



Estimating Runoff. 



area) ; also the mean annual rainfall on the Ashtabula drainage area is 
less than on the comparative drainage area. 

8. Rainfall and Runoff Relations. — With the annual rainfall deter- 
mined from these maps and the annual runoff in inches and in second 
feet determined from the records of runoff (Table 52, Fig. 310) were 
platted to determine the rainfall-runoff relations. On the four dia- 










Fig. 308. — Mean Annual Rainfall at Selected Stations near Ashtabula, Ohio. 

(See page 531.) 



Comparative Hydrographs. 



533 



grams of Fig. 310, 45 ° lines of mean annual retention were drawn (E, 
E) and also lines of mean annual rainfall-runoff relations (G, G) were 
drawn through the center of gravity of the entire series and for the sub- 
groups. Lines were also drawn showing the percentage of departure 
-f- and — from the mean rainfall-runoff relations in Diagrams C and D. 




Fig. 'doy. — Mean Annual Rainfall on Drainage Areas near Ashtabula, Ohio. 

(See page 531.) 

9. Estimated Runoff on the Basis of the Mean Ashtabula Rainfall. — 
On the assumption that the mean runoff on the Ashtabula drainage area 
would bear the same relations to the mean annual rainfall as the mean 
rainfall-runoff relations on the other streams, the runoff corresponding 



534 



Estimating Runoff. 



to a mean rainfall of 40.5 inches was then determined from Fig. 310, 
for each drainage area as follows : 

TABLE 54 

Estimated Mean Annual Runoff from Various Comparative Drainage Areas 
Based on the Mean Annual Rainfall of the Ashtabula River Drainage Area. 



Area Sq. 

Miles 



Rainfall 
Inches 



Runoff 



Inches Second ft. 



Shenango River at Sharon 610 40.5 15.9 i 1.15 

Shenango River at Turnersville 152 40.5 I 19.6 ! 1.42 

Little Shanango at Greenville 107 40.5 \ 18.1 j 1.45 

Cussewago Creek at Meadville I 90 40.5 16.9 | 1.23 







17.6 
18.2 


1.28 
1.37 



10. Estimated Flozv of the Ashtabula River. — It is probable that the 
flow of the Ashtabula River will be greater than that of the three 
smaller streams used for comparison. The average annual flow of 
these three streams is 1.37 second feet. 

The larger area of the Shenango River above Sharon has the small- 
est relative runoff. This might normally be expected both from the 
size of the area and from the geology. Including this area with the 
others, the average annual runoff of the four streams, on the basis of an 
average annual rainfall of 40.5 inches, is 1.28 second feet per square 
mile. 

It will be noted from the mass curves that the only waste of water 
occurs in years of high flow. The mean annual runoff for the period 
of runoff records is 1.40 second feet per square mile. The waste of 
water is shown by a comparison of the mean of Table 53 (1.40) com- 
pared with the mean of Table 52 (1.28) and is equal to 12 second feet 
or to 9% of the average water utilized. The average rainfall creating 
this waste is 42.66" and it seems likely that for an average of 40.5" the 
waste would not be more than 5 % . 

11. Conclusions. — From the data considered it would appear that 
the annual average flow of the Ashtabula River will probably average 
above 1.37 cubic feet per second per square mile of drainage area and 
will be at least 1.31 second feet. This should be reduced by about 9% 
or to 1.2 second feet for safety which, allowing 570 for probable waste, 



Comparative Hydro graphs. 



535 



gives a further allowance for safety of about 4%, or a total allowance 
for safety of at least 20% in the runoff estimates. In this case the 
mean available runoff was the data needed for the purpose of estimat- 
ing whether the average power that could be delivered from the stream 
was sufficient to warrant the expense of installing a hydro electric 

28 
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36 3d 40 42 44 46 48 50 36 38 40 42 44 46 
Pa/'n foil I -Inches on Drainage Area. 

Fig. 310. — Mean Annual Rainfall-Runoff Relations for Streams near Ashtabula, 

Ohio. (See page 532.) 

plant, which, together with the auxiliary power already installed, would 
maintain the total output to an economical maximum which the flow of 
the more productive year might warrant. 

12. Method. — The method of estimating runoff by comparison with 
other streams as outlined above is evidently open to criticism as ap- 
proximate and subject to considerable errors. It is believed, however, 
that the factor of safety used resulted in a conservative and safe esti- 
mate of runoff. This method offers a fairly definite method of proce- 



536 



Estimating Runoff. 



dure which can be applied without radical assumptions and by engineers 
of limited hydrological experience. When time and expense are war- 
ranted, this method can and should be supplemented and the conclu- 




JFig. 311. — Relative Locations of Drainage Areas of the Peshtigo, Wisconsin 
and Menominee Rivers (see pagee 538). 

sions corrected by at least short time observations of streamflow on 
the stream for which the estimates are made. It is also probable that 
a more detailed analysis of the monthly rainfall-runoff relations, some- 
what on the line of the Meyer method, might serve to confirm or cor- 
rect the conclusions drawn. 



Comparative Hydro-graphs. 



537 




M ina'/cates Drainage Area of Menominee Pi ver 
P indicates Drainage Area of Peshtigo Piyer. 
Wind/cafes Drainage Area of Wisconsin Piver 

Fig. 312. — Annual Rainfall on Drainage Areas of Peshtigo, Wisconsin and 
Menominee Drainage Areas (see page 538). 

241. Estimating Available Flow with Moderate Storage from 
Comparative Hydrographs. — In the year 1906 investigations were be- 
gun on the feasibility of developing the Peshtigo River of Wisconsin 
at High Falls (see upper Frontispiece) for power purposes and con- 



538 



Estimating Runoff. 



ducting electrical current to Green Bay to be used, with the stream 
electric plant already installed as auxiliary, for the purpose of furnish- 
ing power and light to that City. Surveys were made from Johnsons 
Falls (about y/i miles below High Falls) to Cauldron Falls (about 
yy 2 miles above High Falls) and as the project looked favorable, a 
gaging station was established near a farm house 9 miles below the dam 
site. In 1908 the question of construction became important and es- 
timates of the probable flow of the stream became necessary. At the 
time this estimate had to be made there were one year's gagings available 
on the Peshtigo River and about five years' gagings on the Wisconsin 
River at Merrill, and on the Menominee River near Iron Mountain, 
Michigan. 

1. Physical Conditions. The relative locations of the drainage areas 
of these streams are shown on the map (Fig. 311). All of the areas 
considered lie within the boundaries of the kettle moraine of the second 
glacial period and within the geological limits of the Archean and Al- 
gonquin Rocks. The Wisconsin drainage area has the greatest amount 
of surface storage in lakes and swamps and considerable deposits of 
sandy soils of the second glacial epoch are found on all three drainage 
areas. 

2. Rainfall. — The distribution of the annual rainfall for the water 
year beginning Dec. 1 and for the five years for which runoff records 
were available and the mean annual rainfall for the years preceding 
1908, are shown on the series of maps in Fig. 312. From these maps 
the mean annual rainfalls on each drainage area for each year, for the 
mean of the five years of runoff records and for the mean of the period 
of rainfall records were determined and are shown in Table 55. 



TABLE 55 
Mean Annual Rainfalls on Peshtigo River and Comparative Drainage Areas. 



Drainage Areas 


1903 


1904 


1905 


1906 


1907 


5- Year 
Mean 


Mean 
Annual 
Rainfall 


Wisconsin 


42.1 
46.5 

46.5 


34 
36 
39.5 


34.5 

36 

39.5 


36 
38 
39 


24.5 
27.5 
32 


34.2 
37.3 
38.2 


* 27.2 
33 


Menominee 


32 







The average annual rainfalls at certain stations adjacent to the three 
drainage areas considered are shown in Fig. 313, page 539. 



Estimating from Comparative Hydrographs. 539 






"> ^» **> *o 
<3 5 <5 <5> 

O) ft) Dj 1) O) 



. /lean Annua/ 




Annuo/ and Seasonal Roinfo// 
on one/ near /he r*Tenominee River Drainage Area 




/lean Annua/ 



r/ean S/ or age 
r/eon Growing 
Mean 
Pep/enishing 



Annua/ and Seasona/ Ra/nfa// 
on and near /he Wisconsin River Drainage Area 




/lean Annual 



/lean S/orage 
/lean Growing 
/lean 
Rep/enishing 



Annua/ and Seasona/ Rom fa// 
on and near /he Resh/igo River Drainage Are a 

I | S/orage Period v%A Growing Period Uli Pep/enishing Period 

Fig. 313. — Annual Rainfall at Stations on the Peshtigo, Wisconsin and Menom- 
inee Drainage Areas (see page 538). 



540 



Estimating Runoff. 



3. Runoff. — A comparison of the hydrographs of the Peshtigo, Wis- 
consin and Menominee Rivers, showing the discharge in cubic feet per 
second per square mile for the year 1907, is shown in Fig. 283, page 487. 



<0 



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s / 



ff— Comporati ve Duration Curves for /907 



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Curves of the Menominee River 








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C.~ Duration Curves of the Wisconsin River 

Fig. 314. — Duration Curves of the Peshtigo, Wisconsin and Menominee Rivers. 

From these hydrographs, corrected for flow under ice conditions, the 
comparative duration curves for these three rivers and for the year 
1907 were made (Fig. 314-A). These duration curves show the same 
data as shown by the hydrographs (Fig. 283) except that the daily 
runoffs are shown arranged in the order of their magnitude. With 



Estimating from Comparative Hydrographs. 541 

the storage available above High Falls, these curves would all be main- 
tained to a minimum of .645 cubic feet per second per square mile. As 
the annual rainfall on the Peshtigo drainage area for the year 1907 
was a minimum for the 16 years of annual rainfall records, and about 
10% below the mean annual rainfall on the drainage area, it seemed 
probable that the flow of that stream for that year reaches a minimum 
that would rarely be reached. It should also be noted that although 
the annual rainfall for 1907 on the Peshtigo River was 10% less than 
on the Wisconsin and 23% less than on the Menominee, the low water 
flow for the lowest six months of the year was well maintained and only 
slightly less than that of the two comparative streams. 

Comparative hydrographs of both the Wisconsin and Menominee 
Rivers were also made and studied. The daily hydrographs for the 
Menominee River are shown in Fig. 315. Duration curves for both 
streams for the five years of records are shown in Figs. 314. 
The rainfall diagrams of Fig. 313, and the Table 55, both show that the 
annual rainfalls for 1903, 1904, 1905 and 1906 on both the Wisconsin 
and the Menominee drainage areas were considerably above the mean 
annual rainfall for the period of rainfall records, but that the annual 
rainfall for 1907 on both areas was much less than the mean and very 
near the minimum for the period of record. 

4. Conclusions. — It was concluded from this study that the average 
flow would probably be at least 10% greater than shown by the 1907 
hydrograph and duration curves ; that there might be years of somewhat 
less flow which could be cared for by the Green Bay steam plant ; that 
the hydrograph and duration curve of the Peshtigo River for the year 
1907 furnished a conservative basis for estimating the average annual 
available water supply ; and that if such as an average would furnish 
an amount of power which would be profitable when the cost of installa- 
tion and operation was considered, then the project was feasible. The 
final conclusions were that a dependable average flow of 377 second 
feet was available which with the 85 foot head, which could be de- 
veloped, would at 80% efficiency produce at the turbine shaft 70,000 
horse power hours per day, and that with the steam auxiliary power 
available at Green Bay it would pay to develop the hydraulic plant to 
to a capacity of 485 second feet or 90,000 horse power hours per day. 

It may also be noted that the plant at High Falls was duly constructed 
(see Frontispiece, lower figure) and has been operated successfully and 
profitably. A hydrograph showing the natural stream flow, the water 
used and the water wasted, as well as the variations in head in the 
reservoir for the year 19 17, is shown in Fig. 278, page 475. 



542 



Estimating Runoff. 




Jan. Feb. Plan Apr. rloy .June Ju/y Aug. Sept, Oct. A/ov. Dec. 
Fig. 315. — Hydrographs of the Menominee River (see page 541). 



Literature. 543 

LITERATURE 

Rainfall and River Outflow in the Mississippi Valley, Thomas Russell, Ann. 

Rept. Chief Signal Officer U. S. A., 1889, Pt. 1, Appendix 14, p. 159. 
The Laws which Govern Stream Flow, C. C. Vermuele, Geol. Survey, New Jer- 
sey, Vol. 3, Water Supply, 1894. 
Forests and Water Supply, C. C. Vermuele, Ann. Rept. State Geol. Survey, 

1899. 
Stream Floio Data from a Water Power Standpoint, C. E. Chandler, Jour. 

N. E. Water Wks. Assn., Vol. 21, p. 464, 1907; also Vol. 22, p. 409, 1908. 
Power Capacity of a Running Stream with Storage, W. G. Raymond, Jour. 

N. E. W. Wks. Ass'n, Vol. 22, p. 184, 1908; also Proc. Iowa Eng. Soc. 17th 

Ann. Meeting, 1905. 
Derivation of Runoff from Rainfall Data, J. D. Justin, Trans. Am. Soc. C. E., 

Vol. 77, p. 346, 1914. 
Computing Runoff from Rainfall and other Physical Data, A. F. Meyer, Trans. 

Am. Soc. C. E., Vol. 79, p. 1056, 1915. 
Poioer Estimates from Stream Flow and Runoff Data, D. M .Woods, Boston 

Soc. C. E„ Vol. 3, p. 77, 1916. 

STORAGE AND PONDAGE 

The Capacity of Storage Reservoirs for Water Supply, W. Rippl, Pro. Inst. 

C. E„ Vol. 71, p. 270, 1883. 
Storage and Pondage of Water, J. P. Frizell, Trans. Am. Soc. C. E., Vol. 31, 

p. 29, 1894. 
A Mathematical Analysis of the Influence of Reservoirs upon Stream Flow, 

J. A. Seddon, Trans. Am. Soc. C. E., Vol. 40, p. 401, 1898. 
The Croton Valley Storage, Samuel McElroy, Jour. Assoc. Eng. Soc, Vol 8, 1889. 
Flow of Streams and Storage in Massachusetts, Desmond Fitzgerald, Trans. 

Am. Soc. C. E„ Vol. 27, p. 253, 1892. 
Rainfall, Flow of Streams and Storage, Desmond Fitzgerald, Am. Soc. C. E., 

Vol. 27, p. 304, 1892. 
Storage Reservoirs in Southern Cal., Robert Fletcher, Eng. News, Vol. 46, 

p. 124, 1901. 
Pondage and Storage, D. W. Mead, Chap. VII, Water Power Engineering, 

McGraw-Hill Book Co., 1915. 
Reservoir System of the Great Lakes of the St. Lawrence Basin, Its Relation 

to the Problem of Improving the Navigation, H. M. Chittenden, Trans. 

Am. Soc. C. E., Vol. 40, p. 355, 1908. 
Effect of Proposed Storage Reservoir on Stream Flow and Water Power of 

Lower Chippewa River, C. B. Stewart, Eng. News, Vol. 70, p. 246, 1913. 
Storage to fee Provided in Impounding Reservoirs for Municipal Water Supply, 

Allen Hazen, Trans. Am. Soc. C. E., Vol. 77, p. 1539, 1914. 
Filling and Emptying Reservoirs, T. R. Running, Graphical Solution, Eng. 

Rec, Vol. 69, p. 67, 1914. 



CHAPTER XIX 
FLOODS AND FLOOD FLOWS 

242. The Importance of Flood Studies. — The problems of flood 
relief with which the engineer has most commonly to deal are the pro- 
tection of populous districts of cities by the construction of storm water 
sewers, and the drainage of agricultural lands by canals and ditches. 
Closely connected with such works are the design and construction of 
channel improvements and levees for the protection of city and agricul- 
tural areas from the flood overflow of creeks and rivers bordering on 
or passing through areas to be protected or improved. Still greater 
problems arise when important communities must be protected from 
the damages occasioned by great floods where conditions must be im- 
proved by still more comprehensive works, including river diversion 
and training works, channel improvements, levees and revetments and 
perhaps the construction of impounding and retarding reservoirs. 

The railroad engineer finds constant need for the study of flood con- 
ditions in order to design the culverts and bridges frequently necessary 
along the railroad rights of way, with sufficient capacity and stability to 
protect tracks and embankments from washouts and .the attendant re- 
sults. In water supply, water power and irrigation work the engineer 
must often design structures to impound, conserve and utilize water 
supplies, and must provide suitable spillways, wasteways and flood gates 
to pass the occasional high flood flows in order to protect such structures 
and the lives and property of the communities lying in the valleys be- 
low. Such works are rapidly increasing in number and importance 
with the growth and development of the country, and the consequences 
of ignoring flood conditions, of understimating flood intensities or of 
improper designs to meet the contingencies of floods are constantly 
becoming more serious and involving almost yearly great losses in prop- 
erty and occasionally large losses in life. 

243. Changing Conditions and Flood Effects. — In general the flood 
plains of streams have been created by the streams themselves and 
channels have been maintained only commensurate with the normal 
floods which annually flow through the channels. The occasional high 
flood overflows the river banks, the extreme flood which occurs only at 
rare intervals may find the channel entirely insufficient (Table 56) and 
overflow the entire flood plains from hill to hill. (Fig. 316.) In the 



Flood Effects. 



545 



TABLE 56. 

Present Channel Capacities in the Cities of the Miami Valley Compared with 
the 1913 Flood Discharge.* 



City 



Channel 
Capacity 
Sec. Feet 



Flood 
Discharge 
Sec. Feet 



Ratio 
Per Cent 



Drainage 

Area 
Sq. Miles 



Sidney 

Piqua 

Troy 

Dayton 

Dayton (Below Wolf Creek) 

Miamisburg 

Franklin 

Middletown 

Hamilton 



10,000 

25,000 

20,000 

90,000 

100,000 

65,000 

65,000 

115,000 

100,000 



44,000 
70,000 
90,000 
250,000 
252,000 
257,000 
267,000 
304,000 
352,000 



22.7 
35.7 
22.2 
36.0 
39.7 
25.3 
24.3 
37.8 
28.4 



555 
842 
908 
2,525 
2,598 
2,722 
2/7.85 
3,162 
3,672 



7dO 
770 
76(? 



_ River 
Channel 



ff.— Cross 5ecf/on of Miami River at Dayton, Ohio 



City of Dayton 




D/Afance-3 - Hundreds of feet: 



30 



Fig. 316. — Extent of Overflow from the 1913 Flood. 



a Report of Chief Engineer, Miami Conservancy District, Vol. 1, p. 26, 1916. 
2 Diagram A from Eng. News, Jan. 4, 1917. Diagram B from Rept. Chief 
Engr., Miami Conservancy Dist., Vol. 1, p. 68, 1916. 
HYDROLOGY — 35 



546 



Floods and Flood Flows. 



settlement of every country the lands first occupied are those that are 
most convenient and favorable for habitation, agriculture, commerce, 
manufacturing and other uses. Submerged lands or lands subject to 
frequent overflow are at first ignored, and those subject to occasional 
overflow may be settled and be abandoned when such overflow occurs, 
or are occupied on account of their otherwise desirable character or 
location in spite of the occasional troubles and losses entailed. 




t 



Pig. 317. — Gully Erosion near Janesville, Wis. 

As communities develop, the existing settlements attract other set- 
tlers and the demands for additional area for habitation, manufacturing 
and agriculture increase land values. Channels that are only occasion- 
ally occupied by the streams and low bottom lands are filled and built 
upon ; bridges are built often without provision for extreme floods ; and 
even the normal channels are sometimes so restricted (Fig. 276, page 
465 ) that the ordinary floods must rise in height in order to create the 
increased velocity needed to carry the water through the reduced chan- 
nel. In many cases the channels of streams through farming districts 
become restricted to a greater extent than those through cities. Im- 
proper methods of cultivation and the diversion of minor drainage to 
new channels often result in undue erosion (Fig. 317) and cause the 
washing into the streams of large quantities of sands and gravels which 
congest the channels (Fig. 318). Caving banks carry stumps and trees 
into the stream, and the channel is also frequently used as a convenient 



Flood Effects. 



547 




Fig. 318. — Bar Formed in the Rock River above Janesville, Wis., due to Erosion 

shown in Fig. 317. 

dumping ground. The result is undue congestion which often becomes 
manifest only under extreme flood conditions (Table 57). 

TABLE 57. 
Present Channel Capacities at Yarious Loations in the Miami Valley Out- 
side of Towns and Cities, Compared with the 1913 Flood Discharged 



Stream 



Location 



Channel 

Capacity 

Second Ft. 



Flood 
Discharge 
Second Ft. 



Ratio 
Per Cent 



Mad River 

Mad River 

Stillwater River. 
Stillwater River . 
Stillwater River. 
Loramie Creek . . 
Miami River 
Miami River 
Miami River 
Miami River 
Miami River 
Miami River 
Miami River 
Miami River 
Twin Creek .... 



West of Springfield . 

Below Osborn 

Above Covington . . . 
Below Covington . . . 
Above West Milton . 
N. W. of Lockington 

Above Sidney 

Above Sidney 

Below Piqua 

Tadmor 

Below Dayton 

Below Miamisburg . . 
Below Hamilton 
Below Miamitown 
West of Germantown 



5,000 

6,500 

1,200 

6,000 

7,000 

1,600 

5,000 

5,000 

10,000 

8,000 

25,000 

35,000 

25,000 

20,000 

3,000 



55,400 

75,700 

33,100 

51,400 

86,200 

25,500 

34,100 

48,500 

70,000 

127,300 

252,000 

257,000 

352,000 

384,000 

66,000 



9.0 
8.6 



3. 
11. 



6.3 

14.7 

10.3 

14.3 

6.3 

9.9 

13.6 

7.1 

5.2 

4.5 



3 Report Chief Engineer, Miami Conservancy District, Vol. 1, p. 25, 1916. 



548 Floods and Flood Flows. 

244. Great Floods and Flood Losses. — The damages occasioned 
by floods are notable on account of their sudden and serious character, 
and while it is probably true that the financial losses occasioned by floods 
are not in the aggregate so large as those occasioned by droughts yet 
the latter are less obvious or determinable and in general more difficult 
to prevent. Floods destroy property and life, and losses are direct 
and measurable. The effects of their recurrence and often of their 
first occurrence can be obviated by proper protective measures, al- 
though in general the shortsightedness of a community in this regard 
is overcome only after actual flood losses have been experienced. 

As examples of the serious nature of flood problems and the neces- 
sity of betterments to prevent the recurrence of such disasters, the 
following data are given concerning a few floods of comparatively re- 
cent times. 4 

In 1791 Great flood occurred in Cuba and some 3,000 lives are said 
to have been lost. 

In 181 1 Some 24 villages were swept away by a great flood of the 
Danube in Hungary. 

In 1813 Some 10,000 lives were lost by floods in Austria, Hungary, 
Poland and Silicia. 

In 1824 Ten thousand lives were lost in St. Petersburg and Cron- 
stadt from a flood of the Neva. 

In 185 1 The Yellow River of China burst its banks and changed its 
course for almost 600 miles, changing its point of discharge from the 
Yellow Sea to a point 200 miles north in the Gulf of Chili. 

In 1856 Flood damaged the south of France to the extent of 
$28,000,000. 

In 1874 One hundred forty- four persons were drowned by a flood 
accompanied by the bursting of a dam on Milk River, Mass., and 
220 lost their lives in floods in Western Pennsylvania. 

In 1889 Much of Johnstown, Pennsylvania, was destroyed by a flood 
which broke the dam on the Conemaugh River, many lives were lost 
and property worth several million dollars was destroyed. 

In 1903 A great flood occurred in Kansas City and on the Mississippi 
River, causing a loss of many millions of dollars. Heppner, Oregon, 
was also destroyed with a loss of about 300 lives. 

In 1910 The Seine flooded Paris and caused a loss of over 
$200,000,000. 

In 191 1 A flood in Freeman's Run caused the failure of a storage 



* Floods — Encyclopedia Americana. 



Flood Losses. 



549 




92° 9/° 9CT 89" 

Fig. 319. — Alluvial Flood Plain of the Lower Mississippi River (see page 550). 



550 Floods and Flood Flows. 

dam with the loss of 87 lives and the destruction of most of the Village 
of Austin, Pennsylvania. Extensive floods causing heavy losses were 
also experienced on various rivers in Wisconsin. 

In 191 3 Great floods occurred in Eastern United States. In the 
great Miami Valley about 400 lives were lost and property valued at 
about $100,000,000 was destroyed. 

The history of the great plains of China from Peking to the Yangste 
River for the last four thousand years is replete with the occurrence of 
floods in which have been lost literally many millions of lives. The 
history of the settlement of the lower Mississippi Valley is a continued 
story of loss of life and property by the almost yearly overflow of that 
river. In some cases floods have been accentuated by the sudden re- 
lease of stored waters from improperly designed dams and reservoirs, 
and occasionally this has been the controlling cause of the great loss of 
life and property. 

Much can be done toward alleviation and prevention of these condi- 
tions by intelligent engineering works if supported by enlightened pub- 
lic opinion. The great increase in these losses with the development 
and growth of the country is creating a constant demand for such 
betterments. 

245. Floods of the Lower Mississippi Valley. — The greatest flood 
problem in the United States is that of the Lower Mississippi Valley. 
(Fig. 319.) This great valley on account of its accessibility by navi- 
gation, its fertile flood plain and temperate climate attracted settlement 
at an early date. The settlement of these lands and their frequent 
inundations by the floods of the river have caused almost annually 
great losses in property and frequent losses of life. This resulted in 
early attempts at local betterments which have Jater been organized 
into more consistent efforts through state and district levee boards and 
later by government assistance through the Mississippi River Com- 
mission. 

The total amount expended on the levees of the lower Mississippi 
up to 19 14 was about ninety-seven million dollars of which the United 
States expended thirty-one millions. Up to June, 1913, the total ex- 
penditures of the United States on this portion of the river was about 
seventy million dollars. 5 The early works of protection were limited 
in extent and the levees were only sufficient for protection against 
moderate floods. Even at the present day the levees have not been 



• r ' Hearings on Bill S. 2, To prevent floods on the Mississippi River, Commit- 
tee on Commerce, U. S. Senate, 63d Cong., 2d Session, pp. 137-175. 



Lower Mississippi Valley. 



551 



built to an elevation sufficient to provide for the maximum flood height 
which must be expected when the works are finally completed and 
rendered permanent by proper revetment and other bank protection. 
The occasional great floods obtain at intervals averaging about once in 
six years (see Floods of +50 feet at Cairo, Fig. 320), although it will 
be noted that they sometimes follow each other annually for two or 
three years. These great floods have frequently destroyed miles of 
levees and inundated great sections of the alluvial valley. The area 
of the alluvial flood plain of the Lower Mississippi subject to overflow 

60 



SO 









ML 


1 

55/5S/pp/ 


1 

River erf Ca/ra,. 


r//. 














IJl . 


1 II 


















Il 1 


ill 1 II 1 




































































































































































U 9 H h n n 1 U 1 i 9 1 E 1 1 1 11 1 1 























^0 



y° 



/0 



~/8Z0 /830 '840 J850 /860 /870 /880 /8.90 1900 1910 /920 

Fig. 320. — Maximum Annual Gage Heights on the Mississippi River at Cairo, 111. 

prior to the construction of the levee system is estimated by the Missis- 
sippi River Commission at 29,790 square miles (Fig. 319). The 
flood of 1897 inundated 13,578 square miles and that of 1913 about 
10,812 square miles. 

The ordinary floods of the Lower Mississippi are caused by the 
normal floods of its various tributaries, the Upper Ohio, the Tennessee, 
the Upper Mississippi, the Missouri Rivers and many minor streams. 
When the normal spring floods on these various tributaries fail to 
synchronize near their crests the floods on the lower river reach only 
normal heights, but where exceptional rains produce high flood condi- 
tions on one or more of these tributaries and these floods synchronize 
with ordinary floods on other tributaries, exceptional floods result in 
the lower river. The heights of the maximum annual floods at cer- 
tain stations on the Mississippi River and its tributaries are shown in 



552 



Floods and Flood Flows. 



J\ 


P 


?«\ \ 


Ni\ 








r lK 




'1 N 


-^Ci 


pyf 


H ! 






r 


— X \ 1 




N 


/ ! 






^ri 








\j 


y^ 


^)V^~ 






)i 
/ 


( i \ 

) i 

/ ' ' 


/ 


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Floods in Wisconsin. 553 

Figs. 320 and 327. The relative gage heights at various stations on the 
tributaries, and the resulting gage heights at Cairo, are shown in 
Fig. 326, and the rainfalls producing the flood of 1882 together with 
the departure of the rainfall from the normal are shown in Fig. 321. 

246. Floods of October, 191 1, in Wisconsin. — The autumn flood 
of October, 191 1, on the Wisconsin River was one of the most severe 
on record for that river. In general floods on the Wisconsin occur 
in the spring (Fig. 327, p. 562). When fall floods occur they are 
always due to a saturated condition of the drainage area from earlier 
rains followed by an unusual intense concentrated rainstorm. In 
this case the rainfall of October 2 to 6 was preceded during the thirty 
days from September 3 to October 1, 191 1, by a somewhat heavy pre- 
cipitation, the distribution of which is shown in Fig. 322 A. The 
heaviest rainfall of October 2 to 6 extended across the upper portion 
of the Black River Valley and as a broad band across a portion of the 
Wisconsin River Valley (Fig. 322 B)) The heaviest portions were 
south of the headwaters of the Wisconsin River (see also Fig. 200, 
P- 339) where a reservoir system has been constructed. 

The progression of the flood wave from this storm is shown by 
hydrographs for different points along the Wisconsin River in Fig. 287, 
p. 493. At Rhinelander, above which most of the reservoirs on the 
river are constructed, there was practically no flood. In this flood a 
dam just below Wausau went out (Fig. 5, p. 27) which undoubtedly 
was one of the causes of the extra rise at Knowlton. At Grand 
Rapids the flood peak followed a little later. Some of the flood gates 
at that point were blown out which added somewhat to the flood heights 
below that point. At Prairie du Sac, where the plant of the Wisconsin 
River Power Company was under construction, the work was flooded, 
the cofferdam destroyed and a large loss entailed. 

The greatest flood loss from this storm occurred on the Black River. 
The first casualty was the failure of the earth dike of the Dells reser- 
voir dam. This reservoir was used for storing water for power pur- 
poses and impounded about 10,000 acre feet. The dam consisted of a 
concrete section and spillway and of an earthen dike with a concrete 
core wall. The break was occasioned by the over-topping of the earth 
section due to inadequate spillway capacity. The concrete section was 
left intact but the earthwork with i.ts core wall was destroyed. The 
failure of this reservoir resulted in the overtopping of the earth section 
of the reservoir at Hatfield, about 4}^ miles below. 

The Hatfield dam consisted of a concrete spillway about 50 feet in 
height on both sides of which was an earth embankment. The spill- 



554 



§ 



Floods and Flood Flows. 




"o vo 



Floods in Wisconsin. 



555 



way which was some 490 feet long was adequate for any normal flood 
in the river and passed about 12 feet of water before the east embank- 
ment was overtopped and destroyed. The flood waters, when they 
passed over the earth section, washed out 500 feet of reservoir em- 
bankment and about the same length of the Green Bay and Western 
Railroad which crossed the Black River at this point. A view of the 
site of the destroyed earth section at Hatfield, taken some time after 




Fig. 323. — Break in Earth Embankment at Hatfield Dam. 

the flood, is shown in Fig. 323, and the water from these reservoirs 
together with the normal flood of the Black River sweeping down on 
the City of Black River Falls about 12 miles below Hatfield, caused 
great damage in that city. 

The dam at Black River Falls during the flood of June, 191 1 (Fig. 
324), carried about 10,000 cubic feet per second with the spillway 
more than filled. A normal high flood flow of about 40,000 cubic feet 
per second must be expected at Black River Falls under extreme con- 
ditions and without floods from breaking reservoirs. The north abut- 
ment of this dam entered a natural bank of earth but did not reach 
rock (Fig. 192, p. 333). The October flood perhaps 80,000 second 
feet, cut entirely around the north end of the dam and overflowed the 
business district of the City. The view of the flood entering the city 
(Fig. 325) shows a three-story hotel with a portion of its walls just 



556 



Floods and Flood Flows. 




Flood Problems. 



557 



falling into the river. The buildings in the business portion of the 
city* resting on sand foundations, melted into the stream and disap- 
peared, and the flood destroyed not only the buildings and their founda- 
tions but the land was entirely washed -away for about two blocks in 
width and for several blocks in length (Fig. 194, p. 334). The wooden 
mill building (Fig. 325) which rested on a rock foundation was not 
seriously injured. Perhaps the best understanding of the nature of 




Fig. 325.— Flood of October 1911 Entering the City of Black River Falls. 

the catastrophe can be gained from Fig. 193, p. 334, showing the city 
before and after the flood. 

247. Other Flood Problems of the United States.— There are many 
serious flood problems in the United States and comparatively little 
has yet been done toward their solution. About 1,700 square miles of 
the valley of the Sacramento River in California has been subject to 
frequent and serious overflow. This problem has been studied by 
various commissions in 1880, 1894, 1904 and 1910 and a considerable 
difference in opinion developed as to the best methods for its solution. 
The. question has now been settled and some work is being done along 
the .lines adopted by the State and Federal authorities. This problem 
is only second to that of the Lower Mississippi Valley. 13 

The great loss in the Miami Valley due to the flood of 1913 has re- 
sulted in the formation of the Miami Conservancy District, and the 



c Flood Control, H. M. Chittenden, International Engineering Congress 1915, 
Waterways and Irrigation, p. 157. 



558 Floods and Flood Flows. 

preparation of the most comprehensive plans for the flood protection 
of that valley that have yet been attempted in any country. 7 These 
works are now (1919) under construction. 

The rainfall which caused the great flood of March, 1913, is dis- 
cussed and illustrated in Sec. 129, p. 266 et seq. and the flood condi- 
tions at Dayton are shown in Figs. 10 and 11, p. 40. The City of Co- 
lumbus and other cities in the Valley of the Scioto River suffered 
seriously in the same flood and preliminary plans for protecting works 
have been made, 8 but differences in opinion as to the nature and char- 
acter of the work have arisen which have prevented the consummation 
of the plans. 

The City of Pittsburg has suffered seriously from the flood of the 
upper Ohio and its tributaries, and comprehensive studies have been 
made of its flood problems 9 but nothing material has yet been done 
toward permanent flood relief. 

At Kansas City the bottom lands along the Kaw River, which are 
the center of transportation, commercial and industrial activity, were 
damaged to the extent of over $30,000,000 and a loss of 19 lives in 
the flood of 1903. 10 While agitation for flood protection has been 
constantly maintained ever since that date no comprehensive plan has 
yet been carried into effect, largely on account of divided jurisdiction. 

248. The Cause of Floods. — The causes that produce runoff and 
its variations have been discussed in Chapters XVI and XVII. The 
causes of high water, excessive runoff or floods should be evident from 
that discussion and may be summarized as follows : 

1. Floods will occur on a given drainage area when the following 
conditions obtain at one and the same time, and will increase in inten- 
sity and duration as the conditions become more favorable to increased 
runoff. 
A. When the rainfall on the drainage area is of : 

a. Great intensity 

b. Wide distribution 

c. Long duration 



i See Report of A. E. Morgan, Chief Engineer, Miami Conservancy District, 
Dayton, Ohio. Also various Bulletins published by the Miami Conservancy 
District. 

s See Report on Flood Protection of Columbus, Ohio, by J. W. Alvord and 
C. B. Burdick, 1913. Also Report on Flood Relief for the Scioto Valley, by 
J. W. Alvord and C. B. Burdick, 191G. 

9 See Report of Flood Commission of Pittsburg, Pa., 1911. 
10 See The Floods of the Spring of 1903 in the Mississippi Watershed, Bui. M, 
U. S. "Weather Bureau, 1904. 



Cause of Floods. 



559 



B. When the surface of the drainage area is impervious from : 

a. Saturation by previous rainfall 

b. Frozen condition of ground 

c. Normal geological structures 

C. When retention is at a minimum on the drainage area from : 

a. Cool weather 

b. Absence of vegetation 

c. High humidity 

In addition to the above, floods sometimes result from or are aug- 
mented by ice and log jams and the failure of reservoir dams. 

2. In the comparison of floods on different drainage areas other 
factors are important : Topography, geology, arrangement of tribu- 
taries, surface conditions, location relative to storm paths and sources 
of vapor, climatic conditions, temperatures, wind velocities, etc. 

The maximum floods on all streams are due to a storm or a series 
of storms that have covered the drainage areas so as to produce a syn- 
chronism in the discharge of the various tributaries whereby the max- 
imum flood accumulates at the locality under consideration. The con- 
ditions preceding maximum floods are more apparent from a study of 
the larger streams where numerous data are available. Fig. 326 shows 
various hydrographs of the Mississippi River at Cairo during the six 
maximum recorded floods that have occurred at that place. For each 
flood at Cairo comparative hydrographs are shown of the Upper Ohio 
at Cincinnati, of the Tennessee River at Chattanooga and of the Missis- 
sippi River at St. Louis. The elements of flow conditions at these 
various stations are given in Table 58. 

TABLE 58. 
Elements of Flow Conditions at and Above Cairo. 



Gaging StatioD 


River 


Drainage 

Area Above 

Station Sq. 

Miles 


Flood 
Stage 
Feet 


Height 

in Stage 

Feet 


Lowest 
Stage 
Feet 


Distance 
Above 
Cairo 
Miles 


Cincinnati, Ohio . . 


Ohio 


72,684 

21,418 

699,000 

203,900 


50 
33 
30 


71.1 
58.6 
41.4 


1.9 

0.0 
—3.1 


500 


Chattanooga, Tenn. 
St. Louis, Mo 


Tennessee .... 
Middle Miss. . . 
Ohio 


505 
191 


Cairo, 111 


Mississippi . . . 


712,700 


45 


54.8 


—1.0 





A Comparison of these six great floods with the normal spring flood 
at Cairo is shown by their hydrographs in Fig. 329, page 565. 



560 



Floods and Flood Flows. 




1662 I I 

ff- Cincinnati. C- 5tl 01/ is. 

B- Chattanooga. D-Cairo 



1837 






1883 


A 








R 


















\ 










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r V B ^ 


i V 








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v 








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c 




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\ 












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1884- 


\ 








1 \ 


\ 








\x 




l\ 


\ 


\ > 


A/7 


i\ 


A 




ley 


i 




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1912 
















a 


















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A 8 


4 \ , 




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c. 
















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1913 




| 


A 


















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A 


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IS 

1 


4 


1 i ! 

1 '. / 




















c 








\0 








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vi 







C 21? 40 60 SO O 20 40 60 30 Q ZO 40 60 30 
Time - Days- 

Fig. 32G.— Hydrographs of Mississippi River at Cairo and of Various Tribu- 
taries during the Six Maximum Floods at Cairo. 



Cause of Floods. 561 

From Fig. 326 it is evident that the crests of the various floods at 
Cairo are due to high water in the tributaries as follows : 

1882 Upper Ohio and Middle Mississippi 

1883 Upper Ohio and Middle Mississippi 

1884 Upper Ohio and Tennessee 

1897 Upper Ohio, Middle Mississippi and Tennessee 

1912 Upper Ohio, Middle Mississippi and Tennessee 

1913 Upper Ohio, Middle Mississippi and Tennessee 

The frequent and excessive floods of the Ohio River result from the 
fact that the normal tracks of storms from the southwest parallel its 
course. (See Fig. 153, p. 274 and Fig. 321, p. 552). 

In all cases it is noticeable that the floods in the Upper Ohio dominate 
the Cairo floods and the exceptional floods are produced by a combina- 
tion of floods in the Upper Ohio with those from one or more of the 
other large tributaries. It is also evident that if a flood ever occurs 
that combines high water in the Mississippi River, such as occurred in 
1844 at St. Louis (Fig. 326, p. 560) with high water in the Ohio such 
as occurred at Cincinnati in 1884, together with the high water that has 
occurred on the Tennessee or some of the other minor tributaries, Cairo 
will experience a flood of a magnitude materially greater than has as 
yet occurred within the period of the limited records. 

An interesting and instructive extension of this study can be made 
by adding to these diagrams hydrographs of other large tributaries to 
the Mississippi River or by confining the study to several of the minor 
tributaries and the main tributary into which they flow. 11 

249. Time of Occurrence. — Any series of hydrographs showing the 
daily runoff from a drainage area (Fig. 284, page 488) will show 
periods of high flow which ordinarily occur at more or less certain dates 
but vary considerably in quantity, and consequently in crest height. 
If the series examined covers a long term of years, occasional floods 
will be found to have occurred at dates quite remote from the date 
of common occurrence. 

In general through the northern part of the United States normal 
floods occur in the spring, for while at that season normal rainfall is 
less in intensity, distribution and duration, than during the summer, 
the ground is then more impervious, evaporation is at a minimum, and 
ground flow from the stored water of winter is at a maximum. Never- 
theless observation will show that occasionally on some streams in these 
parts of the country even higher floods occur at other periods on account 



11 Daily River Stages on the Principal Rivers of the United States, Parts I 
to XVI, U. S. Weather Bureau. Gives gage heights from the earliest records 
to and including 1917. 

Hydrology — 36 



562 



Floods and Flood Flows. 




■ 5i t> iT> ^ "- 0) N ^ °) ""• ^5 K >0 "l lA fh N. 0j (^ Ifj (V) ^ (Jj (V t(\ 

1 ^} \t ^ ^ \t "5 ^ "^ ^ <*> % % t\i <Vi <\J Ai <\j v -s >; w 






Occurrence of Floods. 563 

of occasional abnormal conditions of ground saturation and rainfall. 
Fig. 327 shows the relative dates of occurrence and height of the max- 
imum annual floods on various rivers of the United States. 

250. Relative Time of Occurrences of the Flood Crest in Rivers. — 
In a rising river the advance of the the peak of the flood wave does not 
in general represent the velocity of the flowing waters (Fig. 287, p. 493). 
When a flood advances from the head waters of a stream the advanc- 
ing wave must first fill up the river channel or immediate valley to the 
flood line, hence the peak of the wave at any point farther down the 
river is in general caused by water that has passed any upstream point 
at a time later than the occurrence of the flood crest. 

When the flood* is caused by rains or melting snow more or less 
general in extent, the flood wave may be caused by the local runoff or 
by combined local and headwater runoff, and the peak of the flood 
crest in the lower valley may occur earlier or may be simultaneous 
with the flood crests at points on the upper river. (Fig. 328 ). 12 The 
relative time of the flood crest therefore is entirely a matter of distribu- 
tion of the rainfall or snow that produces the flood and of the flood 
channel capacity. 

Occasionally the sudden advent of large bodies of water into a pool 
or river of low gradient, such as is occasioned by a sudden flood pass- 
ing a high dam into a pool below, will set up waves of translation which 
move with high velocities and much faster than the flowing water. 
These sometimes progress upstream in opposition to a river flow as in 
the case of the arrival of a tidal wave at a river mouth. Mr. Wm. J. 
McAlpine 13 states that a wave of translation in the Black River, occa- 
sioned by the failure of a dam, passed from Lyons Falls to Carthage, 
a distance of 40 miles, in two hours, while the flood wave did not reach 
Carthage until six hours after it first passed Lyons Falls. He also 
states that the sudden discharge of water over the dam at Lowell on 
the Merrimac River due to the closing of the wheels on Saturday 
nights, causes a rise of water fifteen minutes later at Lawrence, thir- 
teen miles below, although floats require twelve hours and more for 
their passage. Mr. J. Scott Russell 14 uses the formula given in Sec. 52, 
p. 92, to calculate the velocity of such waves in canals and rivers. (See 
also Sec. 58, p. 105.) 



12 From unpublished data, Miami Conservancy District, by permission of 
A. E. Morgan, Chief Engineer. 

13 Waves of Translation in Fresh Water, Wm. J. McAlpine, Trans. Am. Soc. 
C. E., Vol. 1, p. 383. 

1 4 Beardsmore's Hydrology, p. 211. 



564 



Floods and Flood Flows. 



Rive ps and Creeks 



C/ties and Towns 




Fig. 328. — Time of Occurrence of the Flood Crest at Various Points on the 
Great Miami River during the Flood of March, 1913 (see page 563). 



Occurrence of Floods. 



565 



251. The Rise, Duration and Recession of Floods. — In the occur- 
rence of floods, the time which is taken for the flood wave at any point 
to rise to its peak, its duration at and above the flood stage, and the time 
required for it to recede depend particularly upon the size and shape 
of the drainage area, the arrangement of the tributaries, the storage, 
and on the distribution, duration and intensity of the rainfall pro- 
ducing it. The floods in large rivers usually rise slowly, endure for a 




January February March April May 

Fig. 329. — Comparative Gage Heights of the Six Maximum Floods at Cairo, 111. 



considerable period and slowly recede, while in small streams the rise 
is rapid, the duration short and the recession rapid. In the great rivers 
(Fig. 329), each period may be several weeks in extent. In large 
streams (draining several thousand square miles) the periods are com- 
monly several days (Fig. 330) while in small streams the periods may 
be only several hours in duration (Fig. 331, p. 567). When no surface 
or subsurface storage exists on a drainage area, and when a stream 
has adequate channel capacity (Fig. 184, p. 326) so that there is no 
overflow and consequent valley storage at flood stages, the time of flood 
advance and flood recession is approximately equal. In most cases 
some storage exists and in consequence flood advance is in general more 



566 



Floods and Flood Flows. 



rapid than flood recession. The presence of storage on a drainage 
area therefore reduces the intensity of the flood peak and prolongs the 
duration of the flow (Fig. 337, p. 575). Both the time of occurrence 
and the duration of floods in any stream vary greatly, however, with 
the intensity and distribution of the rainfall, and extraordinary floods 
may depart radically from the normal. (Figs. 330 and 331.) 



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Fig. 330. — Advance, Duration and Recession of Various Floods at Kilbourn on 

the Wisconsin River. 

The relations between the flood waves and the time and amount of 
the rainfalls producing them are shown for the March, 1913, floods on 
the Scioto and the Miami Rivers in Fig. 332. 

The quantity of flow and the consequent flood height affects the ele- 
vation to which levees and other protecting works must be built, and 
the duration must influence the character of construction in order to 
minimize seepage and prevent destruction. The occurrence and dura- 
tion must also modify the size of reservoirs and detention basins, and 
the peak flow must constitute the basis of spillway design. 



Rise, Duration and Recession of Floods. 567 



March March 

24 Z5 26 27 23 29 30 24 25 26 27 28 29 30 



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March fipril 

Fig. 331. — Advance, Duration and Recession of Flood Waves of March, 1913, 
on Various Streams. After A. H. Horton. 



568 



Floods and Flood Flows. 



The records of flood flows may give the average maximum gage 
height or discharge for a 24-hour period or the gage height and max- 
imum discharge at the time of the flood crest. The latter will exceed 
the former by a considerable percentage and the difference in the 
records should be carefully distinguished. In the flood discharge of 
great rivers such as the Ohio and the Upper Mississippi River the flow 





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March 



Fig. 332. — Relations of Rainfall and Flood Waves on the Scioto and Miami 
Rivers for the Floods of March, 1913. 

and crest height for the day of maximum flood vary but little from 
those at the hour of maximum discharge. In small- streams, however, 
there is a great difference between the average discharge for the maxi- 
mum 24 hours and the discharge at the crest of the flood. The maxi- 
mum crest height and the maximum crest discharge is most important 
in certain engineering problems. Mr. W. E. Fuller gives the follow- 
ing approximate expression for the relations of maximum rate of flow 
to average maximum 24-hour flow. 13 



Q max. = Q 



rhich 



( 



1 + 2M-0-3 



) 



Q m . lx = maximum flood discharge in cu. ft. per second 
Q = maximum average 24-hour discharge in cu. ft., sec. 
M = drainage area of the stream in square miles 



15 Flood Flows, W. E. Fuller, Trans. Am. Soc. C. E., Vol. 77, p. 564, 1914. 



Flood Frequency. 569 

This formula gives values for the maximum flow in terms of the 
average 24-hour flow as follows : 

Drainage Area Maximum 24-hour Maximum Flow 

Sq. Mi. Per Cent. Per Cent, of 24-hour flow 

1. 100 300 

10. 100 200 

1000. 100 125 

This formula, as in the case of all other formulas, must be taken as 
a general expression to which there are numerous exceptions. For 
example, the flood in Schoharie Creek in March, 1913, at Ft. Hunter, 
N. Y. (Fig. 331, p. 567) had a maximum flow of 141% of the maxi- 
mum 24-hour flow. 

252. Flood Frequencies. — From the record of past floods it is evi- 
dent that the average flood to be expected every year is exceeded by 
floods of less frequency that may occur at intervals of five to ten years, 
and that these will be considerably exceeded by greater floods which 
may occur at intervals of from 50 to 100 years, and that still greater 
floods must be expected at longer intervals. It is to be noted that the 
intervals mentioned are merely averages, that there is little regularity 
in the occurrence of floods of great magnitude, and that such great 
floods may follow each other at lesser intervals but that the average 
appearance of the greatest floods is rare but uncertain,. The highest 
flood on record at Cincinnati, Ohio, to that date was the flood of 1882. 
This flood was exceeded by the flood of 1883 which in turn was again 
exceeded by the flood of 1884 which has not been equalled since that 
date. 

In the 103 years of record on the Rhine 10 (Fig. 333) there has been 
one flood above 25 feet, seven floods above 24 feet, eleven floods above 
23 feet, twenty-eight floods above 22 feet, and fifty-nine floods above 
21 feet. 

On the Seine River at Paris no flood 'equal to the flood of 1615 has 
occurred since that date (Fig. 334) 1T The two floods next in magni- 
tude occurred in 1658 and 1910 respectively, while six floods above 25 
feet and fifteen above 20 feet have occurred since 1600. 

The great flood of 191 3 on the Miami River was preceded by a flood 



10 From Decrease of Water in Springs, Creeks and Rivers, Gustave Wex, 
Washington D. C, 1880. 

i" Gage Heights on the Seine River at Paris from paper of M. Belgrand An- 
nals du Ponts et Chaussees, 1852, premier semestre, p. 102. Also Report on 
the Influence of Forests on Climate and on Floods, W. L. Moore, p. 18, and 
Eng. News, Vol. 63, p. 327, 1910. 



570 



Floods and Flood Flows. 



almost as great in 1805 while other great floods of lesser magnitude 
occurred in 1866, 1883 and 1898. 

At Cairo, Illinois, located at the junction of the Ohio and Mississippi 
River (Fig. 319) there have been since 1868 six floods above 52.5 feet, 
(Fig. 326 and 329) ten floods above 50 feet and thirty-two floods above 
45 feet or the bank full stage (Fig. 320). 




7770 1780 J 790 /80O /8/0 /8B0 /830 J840 1850 /860 /870 

Fig. 333. — Maximum Annual Gage Heights on the Rhine River at Emmerich, 

Germany. After Wex. 

Where records of considerable periods are available the frequency 
of floods may be considered mathematically, as was the extreme rain- 
fall records in Section no to 112 inclusive but such calculations must 
not be taken too seriously. 'Mr. L. F. Harza, Engineer of the proposed 

1600 /650 /700 /750 /800 /850 /QOO 

29 

28 

27 
\26 
l5 25 

» 23 
\ 22 

%20 

& /9 

,ts /8 

b ,7 

/6 






Fig. 



-Gage Heights of Maximum Floods on the Seine River at Paris, 
France. 



power development at The Dalles on the Columbia River 18 considered 
the flood flows of the river at the proposed power site by probabilities 
(Fig. 335) and the results would indicate that the great flood of 1893 



is Report on Columbia River Power Project near The Dalles, Oregon, L. F. 
Harza, Project Engineer. Technical Pub. Co., San Francisco, 1914. 

Forests and Floods: Extracts from an Austrian Report on Floods of the 
Danube, H. M. Chittenden, Eng. News, Vol. 60, p. 467, 190S. 



Flood Frequency. 



571 



would not be exceeded more than once in 1,000 years. This flood has 
actually occurred once in the 60 years of record, hence the only safe 
conclusion is that such a flood need not be expected at frequent intervals 
although even a greater one may occur in any year. 

253. Are Floods Increasing in Intensity and Duration? — Much of 
the United States has been settled less than a century and in many 

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F-'erceni-crqe of frequency 

Probabilities of Flood Flows on the Columbia River. 
L. F. Harza. 



99.9 99.99 



After 



cases the maximum flood that must occasionally be expected has not 
occurred since the present communities have become important. In 
other cases serious losses of life and property have occurred and as the 
years pass and importance of the communities increases, more serious 
losses are to be expected. The occasional great flood which only rarely 
swept over the level area of the flood plain did no noticeable damage 
until man attempted to appropriate these areas for his own use, and 
hence the occurrence of these floods passed almost unnoticed and un- 
recorded. When, however, these occasional exceptional floods occur 
on thickly settled flood plains the loss becomes great and unprecedented. 
On account of these losses and the fact that they have never been 
experienced previously in the affected region claims are made that 



572 Floods and Flood Flows. 

floods are increasing in frequency and in height or volume due to the 
changes wrought by man in the settlement of the country. 

The foresters and others interested in reforestation have endeavored 
to show that deforestation has resulted in increased floods and reduced 
low water conditions. Engineers in general, however, are of the 
opinion that deforestation and cultivation have produced no radical 
changes of the kind indicated. 

In general it may be stated that the time of observation in the country 
has been too brief to determine in an entirely satisfactory manner 
whether or not there has been any considerable change in flood height. 
The information available indicates no great changes except those due 
to channel restrictions. In the case of the longest records available 
the information is not wholly reliable for, while the gage readings are 
continuous, it is apparent that the datum or zero of the gage may have 
been sometimes altered either by accident or design. The high flood 
of 1805 preceding the great flood of 191 3 in the Miami Valley, and the 
records of the floods of the Rhine at Emmerich and especially the 
records of floods in the Seine at Paris all serve to indicate the occur- 
rence of great floods but show no evidence of any material change in 
flood heights. 

In many cases flood heights have increased due to the restriction of 
the channel by levees built to prevent overflow or by encroachments 
due to the filling in of low lands for building sites. The general flood 
heights on the lower Mississippi River have been raised in this manner 
by the construction of the extensive levee 'system along that river. 
The flood elevation at Memphis, Tennessee, has been thus increased by 
eight or ten feet. Fig. 336 shows the maximum high waters on various 
rivers of the United States. For the earlier years only maximum 
floods are shown, authentic records of which were preserved on account 
of their unusual character. For the later years annual high water 
elevations are available. These records show no radical changes in 
flood heights but indicate that occasional floods which greatly exceed 
the ordinary annual high water flow must be expected. Such extreme 
floods apparently occur once in fifty or one hundred years, although 
there is no reason to believe that they may not follow each other at 
much shorter periods. On the other hand, the longer experience on 
European rivers seems to indicate that periods of several years of ex- 
cessive floods or of unusual low water frequently occur. 

Probably the most conclusive evidence that there has been no material 
changes in extreme flood conditions is furnished bv the investigation of 



Flood Intensity and Duration. 



573 



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1780 /T90 1800 18/0 /SeO /830 /840 18S0 /860 t870 t880 /890 /900 J9I0 1920 

Fig. 336. — Maximum Annual Gage Heights on Various Rivers of the United 

States. 



574 Floods and Flood Flows. 

M. Ernst Landa, Chief of the Hydrographic Bureau of the Austrian 
Government, in his investigations of the floods of the Danube, 10 with 
special reference to the floods of 1897 and 1899. M. Landa reviews the 
records of the excessive floods of the years 1012, 11 18, 1126, 1193, 
1194, 1195, 1210, 1234, 1235, 1236, 1275, 1280, 1281, 1284, 1285, 1295, 
I3 12 - I3I5' 1316, 1317, 1340, 1342, i359> 1402, 1404, 1405. 1406, 1407, 
1408, 1409, 1434, 1437, 1445, 1464, 1465, 1491, 1499, 1501, 1508, 1520, 
1527, etc. The floods of later years while described in greater de- 
tail in the original report are not mentioned in detail in the translation. 

Mr. Landa's conclusions are as follows : 

"To conclude from this chronological record of the Danube floods 
that these catastrophes have increased in number, extent and frequency 
in modern times would be as absurd as to maintain the opposite. The 
history of the past tells of floods which were not subordinate to those 
of the present in any of the above particulars. Two conclusions clearly 
follow from this retrospect : 

"(a) The floods of 1897 and 1899 were not abnormal or unusual 
phenomena in the history of the river. 

"(b) Regulation works have had absolutely no influence in increas- 
ing the heights of floods." 

General Chittenden in commenting on this report says : 

"The number of floods cited by the author is about 125. Many of 
them were accompanied by ice gorges which render close comparison 
with other floods by means of discharge or gage data rather uncertain. 
A noteworthy feature of the record is the occurrence of flood years in 
groups. In nearly the entire period, high flood years were bunched 
together, showing that precipitation moves in cycles." 19 

254. The Effect of Storage on Flood Heights. — It has previously 
been noted that the effect of ground or surface storage is to reduce 
materially the flood heights (Sec. 203, p. 456), and that high floods may 
be entirely obviated by artificial control (Fig. 274, p. 464) where such 
control is physically possible and financially practicable. From this 
consideration it becomes evident that the relative floods on even ad- 
jacent streams may vary greatly with the natural storage on their 
drainage areas. Mr. W. E. Fuller has considered the effects of stor- 
age on flood conditions under certain assumed conditions which though 
necessarily hypothetical are instructive (Fig. 337). Even where little 
natural storage may exist in the ground or in lakes and swamps, the 



n» Forests and floods, Extracts from an Austrian Report on Floods on the 
Danube, H. M. Chittenden, Eng. News, Vol. 60, p. 4G7, 1908. 



Effect of Storage. 



575 



temporary storage produced by the overflow of river valleys during 
floods will modify to a considerable extent the flood heights and dis- 
charge at points farther down the stream. 

In many alluvial valleys the normal heights of extreme floods cause 
an extensive overflow by which large quantities of water are temporarily 
impounded in the bottom lands until the receding floods allow them to 
drain back into the streams. The amount of such storage in the lower 
Mississippi valley prior to the construction of the levee system was 
enormous (see Sec. 245). 

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Time of Flood tn fiours. 



24 



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32 



Pig. 337.— Effect of Storage on Flood Height. After W. E. Fuller. 



The flood plain of the lower Mississippi River has been built up by 
the deposition of sediment adjacent to the river channel and the bottom 
lands slope back from the channel to a considerably lower elevation 
than the river bank and are drained by various tributaries which enter 
the main river many miles below. The section of the valley from 
Memphis westward to Crowley's Ridge is shown in Fig. 338, from which 
it will be noted that the floods prior to the construction of the levees 
could overflow a section about 37 miles in width. By the construction 
of levees the floods are now retained in the river channel and the conse- 
quent flood heights at Memphis have been increased eight or ten feet 
above the elevation to which they rose in times prior to the construction 
of these levees, as will be noted by reference to Fig. 336. 

When channel improvements are undertaken to reduce or prevent 
overflow in a river valley, the storage which has been hitherto effective 
in reducing flood heights at such times is removed or reduced and higher 
floods will consequently be experienced at points farther down the 



576 



Floods and Flood Flows. 



stream. This is an important matter which is frequently neglected in 
plans for levees and channel improvements. 

In considering plans for the flood protection of the Miami valley, 
a study* was undertaken to determine the maximum discharge that 
would have occurred at Dayton and Hamilton in the 1913 flood if the 
river channel had been improved to a capacity sufficient to permit the 
water to flow directly down the channel without overflowing the flood 
plain. 

The total quantity of water stored above Hamilton at the time of the 
peak of the flood was 568,000 acre feet or about .3 of the total rainfall 
which produced the flood, and equivalent to a depth of 2.9 inches over 
the entire drainage area. 



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40 35 30 25 20 1 5 I P 5 9 

Miles 

Fig. 338.— Profile of the Alluvial Flood Plain of the Mississippi River from 
Memphis, Tenn., to Crowley's Ridge, Ark., along the C. R. I. & P. Ry. After 
Mississippi River Commission. 

With the channels enlarged to confine the entire flood flow to the river 
channel, no storage on the flood plain would obt-ain but the channel 
storage would be increased due to the necessary increase in their capa- 
city ; hence the net amount of storage elimination would be the differ- 
ence between the valley storage which could practically be eliminated, 
and the increased channel storage. The valley storage extended far 
up the tributaries and not all of it would be affected by improvements 
of the main river channel, although the depression of the flood plain in 
the main channel would draw down the flood plain of the tributaries 
to a considerable extent. In this study the assumption was made after 



*This example (see Fig. 339, page 578), is taken from an unpublished study 
of the effects of eliminating storage in the Miami Valley by Assistant Engi- 
neer, K. B. Bragg and is here published by permission of Mr. A. B. Morgan. 
Chief Engineer. 



Effect of Storage. 577 

due consideration, that the reduction in valley storage would equal 
451,000 acre feet or about 80% of the total valley storage. The excess 
channel storage which would be created by the necessary channel im- 
provements was estimated at 194,000 acre feet. This amount deduced 
from the 451,000 acre feet assumed to be eliminated from the overflow 
of the valley would leave a net reduction to be removed by the channel 
of 257,000 acre feet. 

The Miami River began to overflow and the valley storage above 
Hamilton became appreciable when the flow at Hamilton reached a 
discharge of about 40,000 second feet, and reached its maximum about 
34 hours thereafter. As all of the valley storage was empounded with- 
in this time, that part of it which would be eliminated would necessarily 
have to pass Hamilton by the time the flood peak occurred. To de- 
termine, therefore, the resulting maximum flow of water which would 
occur at Hamilton, provided valley storage were eliminated, this addi- 
tional quantity of water must be added to the Hamilton hydrograph 
between the hours when the overflow began and the time at which the 
flood peak occurred. As the flood actually occurred, this valley stor- 
age which would be eliminated by channel improvements was stored 
above Hamilton at the time of the peak and passed through with the 
recession of the flood wave. If the storage were eliminated this amount 
of water would be added to the advancing flood wave or to the front 
part of the hydrograph and would be withdrawn from the receding 
wave or be subtracted from the latter part of the hydrograph between 
the discharge limits of the maximum and the time that the falling flood 
had again reached a discharge of 40,000 second feet, thus keeping the 
total flow between the overflow limits the same. This calculation can 
be made most accurately by graphical methods. The general shape of 
the revised hydrograph was determined from a knowledge of the char- 
acteristics of inflow and outflow curves from retarding basins, and 
the exact dimensions were determined by planimeter by making the 
additions to and the deductions from the hydrograph equal to each other 
and to the amount of storage eliminated (Fig. 339 A). 

From the investigation the maximum flow at Hamilton under the 
improved channel conditions was found to be 500,000 second feet or 
about 150,000 second feet above the flow that actually occurred. 

A similar study was also made of the increased flow at Dayton by 
the elimination of the valley storage above that city which showed an 
increased flow at that place of about 80,000 second feet (Fig. 339 B). 
Hydrology — 3 7 



578 



Floods and Flood Flows. 







































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Effect of Storage. 579 

A study was also made to determine what the additional flow would 
be through Dayton if channel improvements were confined to Dayton 
only, and assuming that the flood plain above the City would not be de- 
pressed, thus eliminating only the valley storage within the city itself. 

The storage in the City of Dayton amounted to 83,700 acre feet and 
the total flow occasioned by its elimination was estimated at 285,000 
second feet or 35,000 second feet greater than the total flood flow 
during the flood of 1913 (Fig. 339 C). 

There are two important points to be noted in connection with the 
matter discussed in this section : 

1st. That the maximum unit flood discharge will decrease with the 
increase in valley storage and that in considering the probable maximum 
flood discharge to be anticipated in any stream at the present or in the 
future, the conditions which now prevail and which may prevail in the 
future must be given due weight. 

2d. That when levees and other works necessary to reclaim low lands 
or to prevent the overflow of cities or agricultural lands are constructed, 
they will if they restrict the channels and reduce overflow, accentuate 
flood heights and increase flood flows ; and it becomes important that 
such effects be anticipated and cared for in the design of such improve- 
ments. 

255. The Intensity of the Flood Runoff of Streams. — In the de- 
termination of the maximum flood flows to be provided for in the con- 
struction of hydraulic works or in determining the intensity of runoff 
which may occur at times of maximum flood, it is necessary that the 
local conditions be investigated in each particular case. Consideration 
must be given to every factor which influences the amount of runoff 
and no unit flood should be adopted as a basis of design without a 
thorough investigation of its applicability to the existing conditions. 
In general, the flood runoff data from the local stream and from other 
streams that are fairly comparative should be correlated and studied. 
The intensity, duration and distribution of rainfalls producing great 
floods on the stream in question and on other streams over which the 
same storm centers pass should be platted and studied, and the maxi- 
mum storm that should be expected at seasons of the year when con- 
ditions favorable to high runoff obtain, should be determined as closely 
as practicable. The adoption of a unit discharge as determined from 
the practice at other places or from runoff formulas, based on unknown 
conditions or on conditions quite foreign to the locality under investi- 
gation, is never excusable although such practices and formulas may 



580 



Floods and Flood Flows. 



Authority 
1. Fanning 



2. Dickens 



3. Ganguillet .. Q 



5. Kuichling 



6. Kuichling . . Q 



7. Murphy and Q 

Others 

8. Fuller Q : , 

Q 
Q„ 

9. Burge Q 

10. Craig Q 



TABLE 59. 
Runoff Formulas for Streams 
Formula 

= 200 MV 6 



4. Italian Q =■ 



500 MV« 

1,421 M 

3.11 + VM 
1,819 M 



0.311 + VM 
44,000 



Original Purpose and Reference 

New England Streams 
Treatise on Water Power En- 
gineering 
Central Provinces India 
Indian Professional Papers 
Swiss streams 
Proc. Inst. C. E., Vol. 71, 1883 

Streams of North Italy 
Report on Barge Canal, 1901 



M + 170 
127,000 

c— 

M + 370 
46,790 



+ 20) M 



Mohawk 
floods 



River occasional 



+ 7.4) M 



= ( h 15) M 

M + 320 
= Ci MO-8 

= Qav (1 + 0.8 log T) 
: = Q (1 + 2M-0-3) 

M 

= 1300 

L-/ 3 

SL J 
= 440C 2 Whyp. log — 
W 
Nomenclature 



Mohawk River rare floods 
Report on Barge Canal, 1901 

General 

U. S. G. S. Paper No. 147 

General 

Trans. Am. Soc. C. E., Vol. 77. 

1914 
Madras Railway, India 
Jackson Hydraulic Manual. 

1875 

Proc. Inst. C. E., Vol. 80, 1885 



Q = Maximum (24 hour average) flood in cubic feet per second 

Qmas = Maximum Flow at Flood Peak in cubic per second 

Qnv = Average Yearly Flood in cubic feet per second 

M = Drainage Area in square miles 

L = Length of Drainage Area in Miles to point of discharge 

T = Number of years in the period considered 

W = Width of Drainage Area in Miles 

Ci = Coefficient which should vary with each stream 

C2 =VP (from 0.68 to 1.95 for small mountain districts) 

V t=a Velocity of approach to point of Discharge 

P = Coefficient (.12 to .18) 

serve as a rough guide in the investigation. It must always be remem- 
bered that each problem is independent and is not subject to a general 
solution. 

After a thorough study of the question and due consideration of the 
best information available, a flood flow may be adopted for the pur- 
pose in question, using a factor of safety as great as the importance of 
the local conditions will warrant. 



Runoff Formulas. 



58 



A large number of empirical formulas which attempt to approximate 
the flood runoff from a given area have been devised. Such formulas 
have usually been developed for certain streams or for certain areas 
in which the streams are believed to possess common characteristics. 
They have seldom been intended for general application to all streams 



200 




IOOO f500 ZOOO 2500 3000 3fOO 

Fig. 340. — A Comparison of Various Runoff Formulas. 



or to streams having widely different characteristics, and when so in- 
tended attempt to accomplish the end by means of radical changes in 
their variable coefficients. Unfortunately the limited applicability of 
such formulas is not always understood and consequently they often 
have been selected without proper caution and used with disastrous 
effects. Some of these formulas are shown in Table 59 and graphically 
in Fig. 340. Each one is based on more or less extended observations 
and is applicable only when used under conditions similar to those for 
which it was devised. Verv few of these formulas take into account the 



582 



Floods and Flood Flows. 




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Runoff Formulas. 



583 



great number of conditions that modify the results. For this reason 
most of such formulas are of little use except for the purpose of rough 
approximation. Fig. 341 shows graphically the formulas of Kuichling 20 
for flood flows under conditions comparable to those in the Mohawk 
Valley, New York, and indicate the data upon which such formulas are 
based. 



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/OOO 2000 3000 4000 5000 6000 7000 8000 9000 / 00.00 //OOO 
Dra/nage fire a - Square M//es = A7 

Fig. 342. — Various Conditions to which Kuichling's Curves do not apply. 

A study of the data platted on this diagram and used as a basis for 
these formulas shows that they consist of most of the records of maxi- 
mum runoff of the streams of the world that were available at the 
time the formulas were devised, and that the conditions of runoff of 
many of these streams are in no sense fairly comparable with those 
conditions in the Mohawk Valley. It would therefore seem that the 
formulas were not intended to be limited to the Mohawk Valley but 
were for general application, and for such purposes they, together 
with other similar formulas, have come to be more or less commonly 



-o Report on New York Barge Canal, 1901. 



584 Floods and Flood Flows. 

employed. That a general use of such formulas is entirely unwarranted 
will be seen from the following illustration of their applicability to two 
areas in northern United States where conditions might easily be sup- 
posed to be somewhat similar to those in the Mohawk Valley, much 
more nearly comparable than many of the areas from which runoff data 
were actually used as the bases of these formulas. 

Fig. 342 A is a comparison of the flood flows of 1913 on the Miami 
and Scioto Rivers and their tributaries with Kuichling's curves and 
shows that if flood protection works on those rivers had been based 
upon the formula for "rare floods" they would have been entirely in- 
adequate. Fig. 342 B is a comparison of the maximum flood flows on 
certain Wisconsin Rivers which shows that even Kuichling's formula 
for "occasional floods" would probably give results too large and re- 
quire works too expensive for that stream. This diagram ?lso shows a 
discharge curve recommended by Mr. C. B. Stewart for application to 
the Wisconsin River at and above Merrill, Wisconsin. 

It may be remarked that even within the State of Wisconsin the 
maximum floods so far experienced differ greatly on different streams. 
The maximum floods on the Wisconsin River are about double those 
on the Rock and Fox Rivers while those on the Black River are about 
fifty per cent, greater than those on the Wisconsin. It therefore seems 
evident that no general solution of the flood problem is possible but 
that each problem should be considered in detail and should be based 
on data that are truly comparable.* 

256. Runoff From City Areas. — In calculating the runoff from 
city areas somewhat different forms of expressions which are also 
applicable to the runoff of streams are used. In these formulas 
(Table 60) the rate of rainfall (see. Sees. 124-128) and the slope of 



*For records of flood flows see: 

Report on the Barge Canal, State of New York, 1901, p. 844 

Hydrology of the State of New York, New York State Museum Bui. 85, 1905. 

Geological Survey of New Jersey, Vol. Ill, "Water Supplies, 1904. 

Reports of Floods, U. S. Geological Survey, Water Supply Papers 88, 92, 96, 
147, 162 and 334. 

Reports on Surface Water Supplies of the United States, U. S. G. S. Water 
Supply Papers. 

Reports of Pennsylvania Water Supply Commission. 

Reports of New York Water Supply Commission. 

Reports of Maine Water Storage Commission. 

Flood Flows, W. E. Fuller, Trans. Am. Soc. C. B., Vol. 77, 1914, Tables 12 to 
27 and Table 37 in discussion of this paper by Mr. Kuichling. 

River Stages, Vols. 1 to 15, U. S. Weather Bureau. 



Runoff From City Areas. 585 

the drainage area are considered as factors, and certain coefficients are 
introduced which should be modified by the local conditions of sur- 
face, storage, topography, etc. The determination of the coefficient 
for local use requires a study of the results which have obtained in 
other places where similar conditions have prevailed and a comparison 
of such conditions with those of the locality for which similar or modi- 
fied results are desired. For the conservative application of these 
formulas to local problems the engineer should refer to their more 
extended discussion in the references given. 

257. Flood Runoff From Drainage Districts. — The flood runoff 
from the low flat lands of drainage districts is from the nature of the 
area drained much less intense than from the normal drainage areas of 
streams. The drainage investigations of the U. S. Department of 
Agriculture furnish much pertinent data concerning actual runoff 
observations in different parts of the country.' 21 In drainage work it 
is generally recognized that the amount of water to be removed from a 
district will increase with the amount and intensity of the rainfall, and 
few attempts have been made to devise formulas of general application. 
In each case it is usual to select or devise a formula that fits the con- 
ditions. (Table 61.) 

In the Mississippi Valley the annual rainfall and in general the in- 
tensity of rain storms increase from the source to the mouth of the 
river, and the runoff of drainage districts will likewise increase. Mr. 
C. G. Elliot 22; has suggested a formula, No. 1, Table 61, for calculating 
runoff to be provided for drainage ditches in swamps and other wet 
lands of the Upper Mississippi Valley where the soils are absorptive 
and easily drained. Such a formula should not be used however ex- 
cept for rough approximations until it is checked for local conditions. 
As the rainfall increases the discharge will increase, so in the swamp 
land of Missouri and the Lower Mississippi Valley higher estimates 
of runoff are found necessary for satisfactory drainage work. 

In the preliminary work of the Drainage Investigations in Northeast- 
ern Arkansas,'- 3 the discharge from the low flat alluvial lands were 



2i See Publications of Office of Experimental Station "Drainage Investiga- 
tions," U. S. Department of Agriculture. 

2- Engineering for Land Drainage, C. G. Elliot, John Wiley & Sons, New 
York, 1912. 

23 A Preliminary Report on the St. Francis Valley Drainage Project in 
Northeastern Arkansas, A. E. Morgan, Circular 86, Office Experimental Sta- 
tion, p. 20, 1919. 



586 



Floods and Flood Flows. 



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588 



Floods and Flood Flows. 



calculated from Formula No. 2, Table 61. For other conditions in 
the same district this formula would not give adequate results. 

"For the more rolling and less sandy land in the east part of Missis- 
sippi County the estimated runoff was increased 50 per cent. For the 
clay soils east of Crowleys Ridge the quantities obtained by the use of 
the formula were doubled in making estimates, and for the slopes of 



TABLE 61. 

Runoff from Swamps and Wet Lands. 

Author Formula Application 

1. C. G. Elliot 20 Upper Mississippi Valleya? absorp- 

q = \- 3.63 tive and easily drained soils 

VM 

2. 0. G. Elliot 24 Northwestern Arkansas^ 

q = ^+6 
VM 

3. Morgan Engineer- 28.0 Mississippi County, Ark. 

ing Co q == \- 7.2 

VM 

4. Morgan Eng. Co. . . 38.0 Cache River Drainage District 

q = -— + 8.0 
VM 

5. S. H. McCrory and 35 Cypress Creek Drainage District, 

others q = Arkansas. 24 

6 vm: 

6. 90 Tentative formula for certain 
q = f- 10 Louisiana districts. (No consid- 

yj^ erable storage in bayous and 

ditches) 

7. 3400 Tentative formula for certain dis- 
q== |- 5 tricts in Florida Everglades 

M + 50 
q =1 sec. ft. per sq. mi., M = area in sq. mi. 

Crowleys Ridge three times the quantities determined by the formula 
were taken as the probable flood runoff."' 3 

It should also be noted that in the actual development of some of 
these swamp lands it was found that Equation No. 2 would not give 
sufficiently high unit discharge for satisfactory drainage and formulas 
Nos. 3 and 4, Table 61, were the basis used by the Morgan Engineering 
Company of Memphis, Tennessee, in their design of the necessary 
works. 

In the report upon the Cypress Creek Drainage District in Desha and 
Chicot Counties, Arkansas, 24 Formula No. 5, Table 61 was used which 
gives materially higher unit runoff for that district ; and in Louisiana, 

-4 Bulletin 198, Professional Papers U. S. Dept. of Agriculture, 1915. 



Runoff from Drainage Districts. 589 

where still more extreme rainfall conditions are encountered, the run- 
off must be estimated on a still higher basis and Formula No. 6, 
Table 61, was used as a tentative basis for the investigation of certain 
districts in this area. Most of the Louisiana districts require the in- 
stallation of pumping plants, and in many cases more or less extensive 
bayous are included within the levied areas. These bayous in connec- 
tion with the ditch system often afford extensive storage which when 
properly utilized reduces the size of the pumping plants which need to 
be installed to keep the land free from water. 

In certain investigations in the Florida Everglades, where rainfalls 
are still more intense than in Louisiana, Formula No. 7 of Table 61, 
was tentatively adopted as a basis for drainage estimates. 

The conclusions to be drawn from an examination of these formulas 
are that such expressions must be chosen or devised for each particular 
district and then represent only their author's conclusions based on more 
or less pertinent data concerning local conditions and local runoff. 

In designing ditches even in the same drainage district or in districts 
closely adjoining, it is not always safe to use the same expression for 
runoff as an area with clay soil will discharge much more water than 
a district with sandy soil, and a different basis must therefore be used 
for the design of the ditches when the condition of soil so requires. 

258. Flood Flows of Small Streams for Determining the Capaci- 
ties of Railway Culverts. — There are comparatively few records of 
the flood flows from small areas the drainage from which must be 
provided for by railway culverts, yet these flows must be anticipated 
in the construction of numerous structures in railway lines. The run- 
off formulas used by a few railroads in determining the area of water- 
ways, together with statements of the confidence placed in the com- 
puted results, are given in the following extracts from the committee 
report on "Roadway," published in the American Railway Engineering 
and Maintenance of Way Association, Vol. 10, Part 2, 1909, to which 
the engineer should refer for a more extended discussion. 

The Pittsburg and Lake Erie Railroad (J. A. Atwood, Chief En- 
gineer) uses Burkli-Ziegler and McMath formulas, obtaining the area 
by survey or from government topographic sheets. Maximum rain- 
fall at 3 inches and C = 0.3. The Burkli-Ziegler formula is used 

only when -_ exceeds unity. 

A. 

The Chicago, Rock Island and Pacific Railroad (John C. Beye, locat- 
ing engineer) determines the area, slope and surface conditions of basin 



590 Floods and Flood Flows. 

by actual survey where practicable, otherwise by maps. The formula 
used in Talbot's 

x = CtfU 

x = area of waterway opening in square feet. 

For flat area C = V 3 

For hilly area C = 2 / 3 

For mountainous area C =1 or more 

The culvert is made 50 to 100 per cent, larger than the formula calls 
for, when possible. 

The Chicago, Burlington and Quincy Railroad (T. E. Calvert, Chief 
Engineer) obtains drainage areas by actual survey or from reliable 
maps. For areas less than 1000 acres, the McMath formula is used : 

Q = 2.0625 V 15 A 4 

For areas greater than 1000 acres 

3000 M 
Q = — 

3 + 2 V M 

The results are relied upon unless recorded high water marks indi- 
cate an extra large waterway is necessary. 

The Missouri Pacific Railway (W. C. Curd, Chief Engineer) de- 
termines areas and surface conditions by survey or from reliable maps. 
No one formula is relied upon but the conclusions are checked up in 
all possible ways. The Talbot, McMath or Burkli-Ziegler formula 
may receive the greatest confidence in determining the runoff, depend- 
ing upon the data. Some excess is always provided, depending upon 
the size and local conditions. 

The Missouri, Kansas and Texas Railway (S. B. Fisher, Chief En- 
gineer) uses Talbot's formula with the value of C as follows : 

Steep slopes C = 1.1 

Medium slopes C = 0.85 

Flat slopes C = 0.60 

The areas and design are changed as appears to be made necessary 
by local conditions. 

The Baltimore and Ohio Railway (J. B. Jenkins, Assistant Engineer) 
obtains traces of former floods, fall and cross section of stream by sur- 
vey. This result is compared with Talbot's formula with a factor 
(C) of 4 or 5 for mountainous, % for hilly, y 2 for medium, %'for 
rolling and % for flat ground, the factor being increased in regions of 
heavy rainfall for shape of basin favorable to rapid runoff, etc. The 
opening is usually made 20% greater than would be required by the 
greatest known flood except when the flood was very exceptional. 



Formulas for Flood Flows. 591 

Practically all the railroads depend somewhat upon the results of 
computations from some one or more of the many formulas for runoff, 
but in practically no cases are these accepted as a final estimate. Con- 
sideration is properly given to the many factors which influence the 
runoff but which make the preparation of any formula extremely com- 
plicated if not impossible. 

259. The Derivation or Selection of Formulas for Flood Flows. — 
From the previous discussion it should be evident that runoff formulas 
should never be used until their applicability to the conditions of the 
problem is determined from authentic data derived from areas having 
similar characteristics and after the most complete practicable investi- 
gation. The formula should then be selected or derived to fit the data 
and conditions with perhaps a reasonable factor of safety. The use 
of such formulas therefore is mainly to adjust conditions or to pro- 
portion works designed to conserve or control flood flows from an area 
different in extent but similar in character to those on which the form- 
ula is based. 

For example, formula 2 in Section 257 was determined from the 
assumption that for an area of 9 square miles the flood discharge would 
equal 40 second feet per square mile and that for an area of 100 square 
miles the flood discharge would equal 19 second feet per square mile. 
Substituting these expressions in the general formula (Type 1) the 
value of x and y can be determined and the corresponding discharge for 
areas of other sizes calculated. If the resulting equation when platted 
does not fit the general condition, a formula of different form may be 
derived from other general equations such as Type 2 or Type 3. 

x 

Type 1 q = — — + y 

V M 

x 

Type 2 q = \- z 

M + y 

x 

Type 3 q = 



y V M 
The student will find it instructive to practice devising such for- 
mulas. For example, a formula of Type 1 may be derived to fit the 
conditions : 



Area 


Discharge 


Square Miles 


Second Feet per Square Mile 


200 


12 


50 


17 



592 Floods and Flood Flows. 

and a formula of Type 2 may be derived to exceed the records of the 
flood flow of the Black River (Fig. 340) by 10% or 25%. Such 
practice will be useful in showing the method of derivation of such 
expressions and in giving a better idea of their true value and of the 
danger in their careless selection and use. 

260. The Economics of Flood Protection Work. — In general the 
maximum flood which may be expected from a given drainage area is 
indeterminate. There are no floods of record so great that it is reason- 
able to conclude that there can be no greater. It is always possible 
that a rainfall of greater intensity, wider distribution and longer dura- 
tion may sometime occur or that other conditions may prevail which 
may create more serious flood conditions than have yet occurred. On 
the other hand, from the data previously considered there is evidence 
that the combination of conditions which produces maximum floods is 
very rare, perhaps once in 500 to 1000 years ; that floods of a lower 
magnitude will occur once in 100 to 200 years ; and that lesser floods 
of various degrees will appear in various shorter periods, not with any 
regularity in occurrence but as an average of past conditions. If the 
engineer attempts to design flood protection works for the greatest 
flood he can imagine, most of such works will be entirely impracticable. 

In the consideration of floods and works necessary to mitigate or 
prevent their undesirable consequences, the engineer must constantly 
keep in mind economic conditions. It is apparent that no works of any 
kind are warranted unless the resulting betterments exceed in value 
the cost of the improvements, and the parties interested are able to 
raise the funds necessary to meet the expense which will be incurred. 
Where such works are undertaken by a community the law requires 
that the benefits which will be derived therefrom must exceed their 
costs and that the cost must not be excessive. 

In the construction of agricultural drainage works it is often in- 
expedient to provide for the maximum flood that may occur even every 
five years. The effect of the temporary flooding of agricultural land 
if for brief periods only is not serious. The interest and maintenance 
costs on works of a capacity suitable for extreme conditions would 
make their construction impracticable and it is better to face occasional 
losses or damages of crops than to attempt such expenditures. For ex- 
ample, Formula 3, Table 61, was used by the Morgan Engineering Com- 
pany for drainage work in Mississippi County, Arkansas, as the best 
which the conditions warranted at the time of construction. As was 
expected, the lower lands are flooded to some extent about once in three 



Economics of Flood Protection. 593 

years and undoubtedly as the lands increase in value the ditches will be 
enlarged so that they will overflow only at rare intervals, corre- 
sponding more nearly with the conditions expressed by Formula 4 of 
Table 61. 

It should be noted in this connection that the damage caused by the 
overflow of levees is much greater than if no levees were in exist- 
ence, and that in most cases economic levee construction should be 
based upon a considerably higher rate of runoff than need be used as a 
basis of canal or ditch design. The probable damages which will be 
entailed in consequence of flooding due to extraordinary storms must 
be kept in mind in all such cases but the physical and financial condi- 
tions of each project will usually establish the limits of expenditures 
beyond which it is impracticable to go. 

In most cases of storm water sewer design the size of the sewers can 
rarely be made adequate to provide for the maximum storm which may 
possibly occur, and a balance must be fixed between the cost of the 
works required to protect the district against floods of a certain magni- 
tude and the damages which may result from storms of greater mag- 
nitude. Commonly the flood which will probably occur once in ten, 
fifteen, twenty-five or fifty years is used as a basis of design according 
to the importance of the interests involved and the comparative costs 
of construction. It may be shown in many cases that the extra cost 
of more extensive work if set aside at interest would accumulate a 
sinking fund in excess of the damage which would be entailed by 
the exceptional flood in which case extra investments are unwarranted. 

In the recent construction of a small water power dam in Central 
Wisconsin it was thought desirable to about double the spillway capa- 
city which had been available and sufficient in case of the old dam 
which had stood for perhaps forty years. It was recognized, however, 
that even the increased capacity of the new dam would be insufficient 
to pass floods which would be occasioned by storms of the intensity of 
that of July 24, 1912 (Table 27, page 248) at Merrill, Wisconsin, or 
that of June 10, 1905, at Bonaparte in Southeastern Iowa (see 
Table 27). In view of the remote possibilities of the occurrence of 
such storms it was necessary to take the chances of such an occurrence 
for otherwise the project would have to have been definitely abandoned 
on account of the great expense involved. 

In more important works where life may be sacrificed by failure and 
where great financial interests are involved, greater factors of safety 
must be used. In the design of the works of the Miami Conservancy 

Hydrology — 38 



594 



Floods and Flood Flows. 



District provisions have been made to protect the District against a 
flood about 40% in excess of the flood of March, 191 3 (Fig. 343 A), 
which is believed to be the maximum flood which can reasonably be 
expected, and the works under construction are designed to sustain 
without injury even a greater flood. 
5 



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to 

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csfimarea Max.. 




















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Flood- 10 in 3 Da us. 




















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1913 Flood 


















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I 2 3 4 5 6 

Days 
ff- Miaimi River af Dayfon, (Phio. B - Scioto River af Co/umbus, Ohio. 

Drainage Area 25 Z 5 5a Mi Drainage Area I6l45a-Mi. 

Fig. 343. — Comparison of Actual Floods of March, 1913, with ideal Maximums 
for which Flood Protection Works are to be designed. 7 ' s 

The proposed works for the flood protection of Columbus, Ohio, also 
provide for a flood of considerably greater magnitude than the maxi- 
mum recorded flood which has occurred at the place (Fig. 343 B). 

LITERATURE 



Yield of the Sudbury River Watershed in the Freshet of February 10-13, 1SS6, 

Desmond Fitzgerald, Trans. Am. Soc. C. E., Vol. 25, p. 253, 1886. 
The Flood in the Chemung River, Report State Engineer, N. Y., 1894, p. 387. 
The Floods of February 6, 1S96, Geol. Survey of N. J., 1896, p. 257. 
Floods of the Mississippi River, Park Morrill, Bui. E, U, S. Dept. of Agric, 1897. 
Report on the Mississippi River Floods, Report No. 1433 U. S. Senate, 55th 

Congress, 3d Session. 
The Floods of the Mississippi River, Wm. Starling, Eng. News, Vol. 37, p. 242, 

Apr. 22, 1897. 
The Mississippi Flood of 1807, Wm. Starling, Eng. News, Vol. 38, p. 2, July 1, 

1897. 
Study of the Southern River Floods of May and June, 1901, Eng. News, Vol. 48, 

p. 102, Aug. 7, 1902. 
The Passaic Flood of 1902, G. B. Holister, and M. ©. Leighton, Water Supply 

and Irrigation Paper No. 88, TJ. S. G. S. 



Literature. 595 

The Passaic Flood of 1903, M. O. Leighton, Water Supply and Irrigation Paper 

No. 92, U. S. G. S. 
Destructive Floods in the United States in 1903, E. C. Murphy, Water Supply 

and Irrigation Paper No. 96, U. S. G. S. 
The Floods in the Spring of 1903 in the Mississippi Watershed, H. C. Frank - 

enfield, Bui. M, U. S. Dept. of Agric, 1903. 
Kansas City Flood of 1903. Eng. News, Vol. 50, p. 233, Sept. 17, 1903. 
Engineering Aspect of the Kansas City Floods, Eng. Rec, Vol. 48, p. 300, 

Sept. 12, 1903. 
Destructive Floods in the United States in 190k, E. C. Murphy, Water Supply 

and Irrigation Paper No. 147, U. S. G. S. 
Flood of March 1907 in Sacramento and San Joaquin River Basins, Cal., W. B. 
Clapp, E. C. Murphy and W. F. Martin, Trans. Am. Soc. C. E., Vol. 61, 
p. 281, 1908. 
The Ohio Valley Flood of March-April. 1913, A. H. Horton and H. J. Jackson, 

U. S. G. S. Water Supply Paper 334, 1913. 
Floods of March. 1913. Bui. Ohio State Board of Health, 1913. 
Floods of 1913 in the Ohio and Lower Mississippi Valleys. A. J. Henry, Bui. Z, 

U. S. Weather Bureau, 1913. 
The Rivers and Floods of the Sacramento and San Joaquin Watersheds, IT. R. 

Taylor, Bui. 43, U. S. Weather Bureau, 1913. 
Flood Control. Los Angeles. Cal. Rept. Bd. of Engineers, 1915. 
Southern California Floods of January, 1916, Water Supply Paper No. 426, 

U. S. G. S., 1918. 
Floods in the East Gulf and South Atlantic States, July, 1916, A. J. Henry, 

Monthly Weather Review, 1916, p. 466. 
Index to Flood Literature, E. C. Murphy and others, Water Supply Paper 162, 

1905. 
Bibliography of Flood Literature. Report of Pittsburg Flood Commissibn, 1912. 
Monthly Index to Flood Literature, Bui. Carnegie Library of Pittsburg, 1908. 

ESTIMATING FLOOD FLOWS 

Determination of the Size of Seivers, R. E. McMath, Trans. Am. Soc. C. E., 

Vol. 16, p. 179, 1887. 
The Relation between the Rainfall and the Discharge of Seivers in Populous 

Districts, Emil Kuichling, Trans, Am. Soc. C. E., Vol. 20, p. 1, 1889. 
The^ Determination of the Amount of Storm Water, Prof. A. N. Talbot, Proc. 

Illinois Society of Engineers and Surveyors, 1894, p. 64. 
The Rainfall and Runoff in Relation to Sewerage Problems, W. C. Parmalee, 

Association of Engineering Societies, March, 1898, p. 204. 
Storm Floivs from City Areas and The Calculations, Ernest W. Clarke, Eng. 

News, Vol. 48, p. 386, 1902. 
Areas of Water Ways for Culverts and Bridges, G. H. Bremmer, Jour. West. 

Soc. Engrs., Vol. 11, p. 137, 1906. 
The Runoff in Storm Water Seioers, C. E. Gregory, Trans, Am. Soc. C. E., 

Vol. 58, p. 458, 1907. 
The Best Method for Determining the Size of Water Ways, Report of Com- 
mittee on Waterways, American Railway Engineering and Maintenance 

of Way, Bui. 108, p. 89, 1909. 



596 Floods and Flood Flows. 

The Sewer System of San Francisco and a Solution of the Storm Water Flow 

Problem, C. E. Grunsky, Trans. Am. Soc. C. E., Vol. 65, p. 294, 1909. 
Runoff from Sewered Areas, L. K. Sherman, Jour. West. Soc. Engrs., Vol. 17, 

p. 361, 1912. 
Discussion of Rainfall and Its Runoff into Sewers, S. A. Greely, Jour. West. 

Soc. Engrs., Vol. 18, p. 663, 1913. 
Flood Flows, W. E. Fuller, Trans. Am. Soc. C. E., Vol. 77, p. 564, 1914. 
A Method of Determining Storm Water Runoff, C. B. Buerger, Trans. Am. Soc. 

C. E., Vol. 78, p. 1139, 1915. 



CHAPTER XX 
THE APPLICATION OF HYDROLOGY 

261. Fundamental Consideration. — Hydrology and all other ap- 
plied sciences must be regarded as a means to an end and not as an end 
in themselves. The only reason for any engineering construction or for 
any engineering project is that as a result sufficient benefit will accrue 
to some individual or to some group of individuals to warrant the ex- 
pense involved. As a consequence of this truth, in the application of 
the principles of hydrology to the work of the engineer, all conclusions 
must be modified by the various factors which influence each particular 
project for the utilization or control of water. 

In general, the factors to be considered in addition to or concurrent 
with the principles of Hydrology are as follows : 

I. Available Funds: Sufficient funds must be available to meet the cost 

of the project. 

(a) Amount will modify possibilities, extent and character of en- 

tire development. 

(b) Source, taxation, special assessment, bonds, stocks, voluntary 

contributions. 
The possibility of securing funds by taxation and assessment depends 
on the laws of state, and the amount which may be raised by this means 
depends on the assessed valuation of the property to be taxed for the 
improvement. The possibility of financing by sale of stocks and bonds 
depends on the value of the property involved in the project, the laws 
under which they may legally be issued and the income which may be 
earned by the property or the returns which may accrue from legal as- 
sessments. 

II. Purpose Served: The project must serve some useful purpose. 

(a) Public service (water supply, water power and navigation). 

(b) Maintenance or improvement of sanitary conditions and pub- 

lic health (sewerage, drainage). 



598 Application of Hydrology. 

(c) Betterment of physical conditions and increase in real estate 

values (irrigation and drainage). 

(d) Protection of life and property (flood protection). 

III. Physical Conditions: The conditions which obtain should be favor- 

able to moderate cost, safe construction, reasonable mainte- 
nance and free from serious contingencies. 

(a) Methods, materials, equipment and machinery available for 

the proposed development. 

(b) Comparative security of structures and methods available. 

(c) Comparative economy of various types of structures and 

methods. 

(d) Contingencies of construction, maintenance and operation. 

IV. Economic Considerations: A comparison of costs and benefits. 

The benefits from the project must equal or exceed the costs. 

(a) Costs. 

Capital Costs : Real estate, Construction, Interest and De- 
velopment expense. 
Operation, maintenance and depreciation expense. 

(b) Benefits: Income from project, Increase in values (of real 

estate), Improvement in health and living conditions and 
Protection of life and property. 

When benefits can be estimated either as annual dividends or as in- 
crease in real estate values, a comparison of such benefits with the costs 
and contingencies involved, will furnish a fair criterion as to the ad- 
visability of the project. The maintenance or improvement to health 
and the protection of life and property cannot always be given a mone- 
tary value, but the desirability is easily established and the financial 
limitations are often quite obvious. 

The study of each of the factors above outlined requires technical 
training, knowledge and experience. The details are so numerous that 
only a few items can be discussed in order to give the student the idea 
of how various factors must influence hydrological deductions. 

262. Applied Hydrology. — In general engineering work in which 
hydrology plays an important part may be divided into : 
I. Works for the utilization of waters ; and 
II. W r orks for the control of waters. 
In most projects, however, both utilization and control may be im- 
portant. 
I. Projects for the utilization of waters may be divided into : 



Water Supply. 599 

A. Private and public water supplies for domestic and manufactur- 

ing purposes. 

B. Irrigation of agricultural land. 

C. Water power. 

D. Internal navigation. 

II. Projects for the. control of water may include : 

a. The drainage and sewerage of cities. 

b. The drainage of agricultural lands. 

' c. Works for the flood protection of cities, communities and lands. 

In the following sections each of the principal classes of hydraulic 
work to which the principles of hydrology most directly apply is briefly 
considered, some of the main factors which may modify hydrological 
conclusions are briefly discussed, and an outline is given which con- 
stitutes an analysis of the main factors which should be considered in all 
projects of the class discussed. The table of literature that follows the 
chapter gives a few of the principal books and articles in which these 
matters are discussed at greater length. 

263. Water Supply. — Water is primarily more essential than food, 
for distress will be entailed earlier from a scarcity or absence of water 
than of food. Both water and food must be available however if life 
is to be maintained in any locality. Every home, farm or community 
of any kind must be provided with water if it is to be even temporarily 
established. The securing of a water supply may therefore be con- 
sidered as the most important object of applied hydrology. 

In the application of hydrological principles to the problem of the 
development of a water supply two main questions are involved which 
are in turn greatly modified in their application by other variable con- 
ditions. These main questions are quantity and quality of the avail- 
able supplies. 

The question of quantity while no more important than that of qual- 
ity, is ordinarily the first to receive consideration, for in every prob- 
lem of water supply it is of primary importance that there shall be a 
sufficient supply for the purposes under consideration or the purpose 
must be modified if the quantity needed cannot be obtained. In de- 
termining quantity both present and future conditions must receive con- 
sideration (see Sec. 210, p. 473). 

A common error in the selection of sources of water supply has been 
the consideration of only the most obvious source and the neglect or 
elimination of other sources less obvious but possibly of greater relative 
importance. It is uniformly desirable that every source which will 



600 



Application of Hydrology. 





D,- Deep Sandstone We//s 
w/'th 
Independent Pumps to Reservo/r 



Pumping Sfof/'on 



• Dr///ed by /9I5 
9 Dr/l/ed by /920 
" Dr/l/ed by J950 



3P 



Fig. 344. — Possible Sources of Water Supply for Rockford, Illinois. 



Water Supply. 



601 



Auburn St. 




• Wel/s Drifted by f9/5 
© Wef/s Drifted by /920 
O Wefts Drit/ed by f950 



£.- Deep Sandstone We//s 

with 
Jndependen t Pumps to Main 



W-9-l 




We//s Drifted by /9/5 
Wef/s Drifted by f920 
Wef/s Drifted by /9SO 



DDDDQ 



nnnn 

Shaft and Tunnet System 

with 

Deep Sandstone Wefts 



Fig. 345. — Possible Sources of Water Supply for Rockford, Illinois, 
yield a sufficient quantity and which seems reasonably feasible of de- 
velopment should be considered. In considering such various sources 
it is necessary to take into account not only the quantity obtainable 
from each but also the methods by which each can be developed and 



602 Application of Hydrology. 

made available and the expense involved in the same. This will neces- 
sarily include the consideration of such processes as may be necessary 
for improving the quality to make each source unobjectionable as a 
water supply for the use and purposes contemplated. It is quite ob- 
vious that in many cases sources which are possible will be shown on 
brief investigation to be impracticable on account of the expense or 
other factors involved. Such sources can then be eliminated from 
further consideration and only those sources which are fairly compara- 
tive or unquestionably desirable may be reserved for final consideration 
and analysis. 

264. Comparison of Sources of Water Supply. — I. Sources. — As 
an example of the various sources and methods of development which 
are sometimes available, the main possible schemes for a water supply 
for Rockford, Illinois, are shown in Figs. 344 and 345. These schemes 
include four different sources, viz. : 

1. Gravel water from the drift (Fig. 344A). 

2. River water filtered (Fig. 344B). 

3. Spring and creek water filtered (Fig. 344C). 

4. Artesian water from the Potsdam and St. Peter sandstone, de- 

veloped by three different methods : 

a. By low lift pumps into a reservoir (Fig. 344D). 

b. By high lift pumps directly into the water mains (Fig. 

345E). 

c. By a shaft and tunnel system pumping from the wells 

either into a reservoir by low lift -pumps or directly into 
the water mains by high lift pumps (Fig. 345F). 

II. Quality. In the comparison of these sources and methods of 
supply, quality must be considered and it is to be noted that in the Rock- 
ford problem the filtration of either the creek (Fig. 344C) or river 
(Fig. 344B) water was contemplated. The artesian water possesses 
the advantage of organic purity but is harder than the creek or river 
water. The gravel water is also open to the objection of still greater 
hardness. In some cases where the softening of the water is essential 
or desirable, the cost of softening should aJso be contemplated in such 
a comparison. 

III. Equipment. In the comparison of sources and methods of de- 
velopment, the type of equipment which is or may be made available 
for the development is an important factor which modifies : 

1st. The reliability of the development. 
2d. The capital cost of development. 



Water Supply. 603 

3d. The cost of operation and maintenance. 

It is obvious that these factors cannot be discussed in detail in a text 
on hydrology, but it seems pertinent to point out that if a dependable 
source can be obtained of satisfactory quality and of a sufficient height 
to be supplied by gravity the cost of operation will be less, and there 
are many other advantages over a supply where machinery is necessary 
to produce the pressure at which the water must be delivered. On the 
other hand, the cost of development of the gravity supply, on account 
of distance from the source, may render the project too expensive for 
consideration, and the adoption of a pumping project may be necessary 
for financial reasons. Again, in pumping projects the relative reliabil- 
ity of the machinery to be used, the expense of operation, and the con- 
tingencies of maintenance may greatly modify the value of one source 
as compared with another. 

In the same way, the necessity of clarification, filtration or softening 
plants involves complications, contingencies and expenses which will 
materially modify the choice of a source. The selection of a source 
may also be greatly influenced by the necessity of storage and the sites 
available for reservoirs, each of which will affect the expense of de- 
velopment. 

The above comments will be sufficient to point out a few of the vari- 
ous modifying influences which must be considered in the selection of a 
source of public water supply in addition to the principles of hydrology 
which have been previously discussed. In general, the principal factors 
to be considered in every water supply problem are outlined in the 
following section. 

265. Outline of Factors for Public Water Supply Investigation. — 

I. Purpose. 

1. Uses of and necessities for water supply: A domestic, B manufac- 

turing, C sanitary, D agriculture, E fire protection, F ornamental. 

II. Supply. 

2. Sources of water supply: A rain water, B rivers, C lakes, D ground 

waters. 

3. Character of supply: A quantity, B quality. 

4. Quantity: A population, past and prospective, B variation in de- 

mand, seasonal, hourly, fire, C regulation by storage. 

5. Quality: A improvement of quality: (sedimentation, coagulation 

and subsidence, aeration, filtration, hardening, softening, sterili- 
zation). 

6. Method of supply: A gravity, B pumping. 

7. Character of service: A constant, B intermittent, C high pressure, 

D low pressure. 



604 Application of Hydrology. 

III. System. 

8. Pumping plants: A primary and secondary pumping, B sources of 

power (water, coal, gas, oil, wind, electricity) C accessories 
(buildings, boilers, producers, motors, pumps, governors, relief 
valves). 

9. Aqueducts, tunnels and conduits for collection and transmission 

(concrete, masonry, wood, iron). 

10. Pipes, distribution: A cast iron, B wrought iron, C steel (riveted, 

spiral riveted, welded), D wood, E lead. 

11. Accessories: A hydrants (gate or valve), nozzles (single, double, 

steamer , B valves and valve boxes, C air valves, D relief valves, 
E service meters. 

12. Appurtenances: A filters and works for clarification, B reservoirs 

and works for storage, C elevated tanks and standpipe. 

13. Design and Construction (present and future requirements), A water 

supply system, B pumping system, C power house, D reservoirs 
and basins, E filters and methods of clarification, etc., F trans- 
mission and distribution systems ( pipes, hydrants, valves, serv- 
ices, meters, plumbing). 

IV. Cost Estimates. 

14. Land and water rights: A rights of way, B condemnation, C dam- 

ages. 

15. Promotion, administration, engineering, supervision, legal expenses. 

16. Time of construction and interest during construction. 

17. Cost of structures: works and overhead costs. 

18. Expense of developing business. 

19. Cost of financing: Discounts, interest and sinking fund. 

20. Maintenance, depreciation, operation, contingencies. 

21. Estimated returns: gross and net profits from projects. 

V. Management. 

22. Private or municipal ownership: A supervision, B office, C field, 

D plant, E books, F records, G rules and regulations. 

VI. Financial. 

23. Financing: A development expense, B operation. C maintenance, 

D depreciation, E valuation. 

VII. Final Conclusion. 

24. Comparative data, general discussion, recommendations. 

266. Irrigation. — I. Application. — In arid regions agriculture can 
be carried on only by means of irrigation, and as the sources of water 
supply in such regions are from the nature of the regions very limited, 
the amount of land which can be made available for agriculture by irri- 
gation is also very limited and will become more and more important 
and valuable as the populations of such regions increase. 

In semi-arid regions crop failures in the absence of irrigation are fre- 
quent and irrigation is usually essential to profitable agriculture. When 



Irrigation. 



605 



irrigation is impracticable, dry farming methods, which are largely 
methods for the conservation of the soil water, are sometimes found 
feasible. In thickly populated humid regions intensive agriculture 
can be carried on only by means of irrigation, and in the suburban 
gardens surrounding large cities irrigation methods established at con- 
siderable expense are amply warranted. 

II. Extent. — The extent to which irrigation has been developed in 
the United States and the character of the various enterprises are in- 
dicated by the 1910 Report of the U. S. Census Bureau (Table 62) 
which however includes only the large projects of the Western States. 

TABLE 62. 

Extent and Character of Irrigation Enterprises in the United States in 1910. 

Acreage 
Acreage Capable of Acreage 

Character of Enterprise Irrigated Irrigation Included 

in 1909 in 1910 in Projects 

Carey Act 288,553 1,089,677 2,573,874 

U. S. Reclamation Service 395,646 786,190 1,973,016 

U. S. Indian Reservations 172,912 376,576 879,068 

Irrigation Districts 528,642 800,451 1,581,465 

Co-Operative Enterprises 4,643,539 6,191,577 8,830,197 

Individual and Partnership En- 
terprises 6,257,387 7,666,110 10,153,545 

Commercial Enterprises 1,451,806 2,424,116 5,119,977 

13,738,485 19,334,697 31,111,142 

An idea of the extent of work involved in the irrigation of this land 
can be gathered from Table 63 which gives the U. S. Census Summary 
of Irrigation Statistics for 1910. 



TABLE 63. 
Summary of Irrigation Statistics for the United States in 1910 {Not 
areas devoted to groioing rice) U. S. Census 1910. 

Total Acreage Irrigated 13,738,485 

Total Acreage that could have been irrigated 19,334,697 

Total Acreage Included in Projects 31,111,142 

Number of Irrigation Enterprises 54,700 

Length of Canals and Ditches 125,591 

Length of Main Canals and Ditches 87,529 

Length of Lateral Canals and Ditches 38,062 

Number of Reservoirs __ 6,812 

Capacity of Reservoirs 12,581,129 

Number of Flowing Wells 5,070 

Number of Pumped Wells 14,558 

Number of Pumping Plants 13,906 

Aggregate of Power used in Pumping 243,435 

Acreage Irrigated with Pumped Water 477,625 

Acreage Irrigated from Flowing Wells 144,400 

Aggregate Cost of Irrigation Enterprises $307,866,369 

Average Cost per Acre $15.92 

Average Cost of Operation and Maintenance per year 1.07 



including 

acres 
acres 
acres 
acres 
miles 
miles 
miles 
miles 
acre feet 



H. P. 

acres 
acres 



per acre 



606 



Application of Hydrology. 



Fig. 346 shows the location of the various irrigation enterprises of 
the U. S. Reclamation Service. Up to June 30, 19 16, there were 
1,405,452 irrigable acres on these projects 922,821 of which were 
irrigated during the preceding year, and there had been expended on 
these projects a total of $149,786,534. The value of the total crops 
raised on all of the reclamation projects in 1916 was $32,815,972. It 




Pig. 346. — Principal Projects of the United States Reclamation Service. 

was estimated by Secretary Lane, in his annual report for the year end- 
ing June 30, 19T8, that there are 15,000,000 to 20,000,000 acres of arid 
land at present in the West for which water can be made available by 
proper conservation. 

III. Profit from Irrigation Developments. — Properly planned irri- 
gation enterprises have proved very profitable and have been of great 
value to promoters, irrigators and to the Nation. Suitable desert land 
which can be purchased under certain legal restrictions at low cost 
(sometimes as low as $1.25 per acre) becomes worth from $50 to $100 



Irrigation. 607 

per acre and upward when successfully irrigated. The costs of irriga- 
tion work vary widely from as low as $5.00 per acre to $100 per acre, 
and more. The margin of profit between cost of land plus a low cost 
of development and the high values of the best irrigated farms seems 
to offer opportunities for high returns, and these opportunities have 
induced promoters to undertake many ill advised, ill! designed and 
unfortunate ventures until at the present time (1919) irrigation pro- 
jects and irrigation securities are looked upon with suspicion by in- 
vestors. 

IV. Causes of Irrigation Failures. — Irrigation failures have resulted 
from many reasons but the most common cause of failure has been in- 
adequate water supply. 'In general these failures have resulted from 
dishonesty and incompetency in management or from mistakes in 
judgment which are exhibited in some of the following ways : 

Inadequate water supply 

Inadequate plans 

Poor construction 

Excessive cost 

Slow colonization 

Excessive distance from market 

It is apparent that an adequate supply of water for a suitable body 
of land is the primary requisite for successful irrigation, and most of 
the principles treated in the text covering the sources, qualities and 
quantities of water apply directly to this phase of the subject. An 
adequate and satisfactory supply is only one phase of the subject; the 
water must be properly conserved and transported to a suitable area 
to be irrigated. As the irrigation season is essentially the growing sea- 
son, adequate storage is often essential to store the supply during the 
months when it is not needed so as to concentrate the supply and adapt 
it to the largest possible area during the irrigation season. This neces- 
sitates an adjustment between the supply and storage, the loss from 
evaporation, seepage, etc., and the demand. The study of these factors 
in relation to the supply of Salt River Project of the U. S. Reclamation 
Service is shown in Fig. 347 as applied to the flow at the Roosevelt 
Dam and its normal application to 161,111 acres of this project. Seep- 
age must be considered not only as it affects the storage of water but 
also as it modifies the losses in transmitting it from reservoir to field. 
In many cases this transmission loss is enormous, and an adequate sup- 
ply at the field to be irrigated frequently requires twice the required 
amount delivered from the reservoir. Soil and subsoil conditions are 



608 



Application of Hydrology. 



therefore equally important to the water supply, for the soil must not 
only be suitable for irrigation purposes but the physical condition 
largely modifies the amount which must be supplied to meet the de- 
mand of the necessary losses in transmission and application. The 
topographical and physical conditions also affect the ultimate success 
for in many cases irrigation and especially over-irrigation results in a 
rise in the ground water and the deposit of alkali on the surface, and 
this necessitates the development of drainage or it results in the ruin of 
the land for agriculture, a consequence often apparently remote before 
land is irrigated but a consequence to be foreseen and considered in the 
intelligent development of plans for irrigation. 



Wafer Wasted over Sp/llway_ 






<J 



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Fig. 347.---iAnalysis of Supply and Demand on the Flow of the Salt River as 
Modified by the Roosevelt Reservoir, when applied to 161,111 acres at the 
rate of 4.5 acre feet per acre.* 



In connection with the development of irrigation and drainage pro- 
jects a question of vital importance to financial success lies in the time 
which it takes to colonize the land and get it under successful cultiva- 
tion. Colonization depends not only on an adequate supply of suitable 
lands economically developed but a 1 so on the demand for such land, 
proximity to a market and other factors which influence or control the 
probable profit to the settler who is to make the project his home and 
on whom the ultimate success of the project must depend. 

Colonization is often a slow process and the profit which apparently 
should result in a great financial success may prove a financial failure 
on account of high carrying charges due to slow colonization. The 



*See Salt River Project, Arizona, Limiting Area of Land, Dept. of In- 
terior, U. S. Reclamation Projects, 1914, Washington, D. C. 



Irrigation. 



609 



average time to colonize various irrigation projects, based on experi- 
ence up to 1910 as derived from the 1910 U. S. census returns, is 
shown in Fig. 348. and the results anticipated and realized from such 
slow development is illustrated in Table 64. This table illustrates the 
possibility of failure through delayed colonization of a project which 

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Pig. 34S. — Diagram Showing Colonization of Average Irrigation Project Ac- 
cording to U. S. Census Returns of 1910.* 

might otherwise have been very profitable, and shows how factors other 
than those of hydrology or engineering must often influence and con- 
trol a project. 



267. Outline of Factors for Irrigation Investigations. — 

I. Location of Project. 

1. With regard to transportation and market, railroads, roads, near- 
est large cities and population, location of other projects, com- 
petition for sale of lands and sale of produce. 



*See Eng. News, Vol. 76, p. 202. 
Hydrology — 39 



610 



Application of Hydrology. 






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Irrigation. 61 1 



II. Physical Conditions. 

2. Topography, geology, altitude, climate, temperature, rainfall (dis- 

tribution through years, variation, extremes). 

III. Land. 

3. Quantity, availability, physical condition, nature. 

4. Character of soil and subsoil: A alkali, B drainage, C seepage, 

D desirability or need of irrigation, E nature of vegetable growth, 
F clearing and grading, G ownership, H legal status, I value or 
cost. 

IV. Surveys, Topographic and Hydrographic. 

5. Land surveys: A canal and ditch location, B farm unit subdivision, 

C town sites, D telephone lines, B roadways, F railroads, etc. 
G. Surface water: A flow of streams (records and gagings), B drain- 
age area (character and topography), C rainfall (comparison of 
rainfall and flow with other longer records), D reservoirs. 

7. Ground water: A depth to water surface, B nature of water bear- 

ing strata, C data. 

8. Water requirements: A estimated quantity, B development, C works 

needed (intakes, galleries, reservoirs). 

9. Pumping water: A methods, B character of fuel, C cost. 

10. Character of water: A salts contained, B silt in flood and normal 

flow, C character and effect of silt. 

11. Water laws: A legal rights, B prior appropriations, C adjudications, 

litigations. 

V. Duty of Water. 

12. Character of crops, water requirements of crops, irrigation season, 

load factor, soil conditions as affecting seepage and evaporation, 
drainage, methods of using, methods of distribution. 

13. Losses in distribution, seepage losses, amount needed at source, 

amount needed at field, total water requirements. 

VI. Development Works. 

14. Diversion works: A dams (dimensions, foundations spillway, over- 

fall, gates, apron). 

15. Storage works: A reservoirs (geology, materials, seepage, cores, 

slopes, protection). 

16. Controlling works: A head gates, B by pass, C overflow wasteways, 

D drops and chutes, E weirs, modules and meters. 

17. Transmission works: A flumes, B tunnels, C canals, laterals and 

ditches (size, length, grade, character of soil, erosion, seepage, 
lining). 

18. Transportation: A railroads, B roads, C bridges, culverts. 

19. Pumping plants (condition, kind, class, power, fuel). 

20. Drainage works: A ditches, B tile. 

21. Auxiliary works, water power development (electric power, pump- 

ing). 

VII. Labor and Materials. 

22. Methods: A contract, B day labor. 



612 



Application of Hydrology. 



23. Labor: A nationality, B availability, C cost, D teams. 

24. Material: A sources, B distance, C cost at source, D cost f. o. b. 

railway, E cost of transportation. 

25. Machinery and equipment required: A class, B source, C cost, 

D hauling. 

VIII. Cost Estimates. 

26. Land and water rights, cost of promotion, administration, engineer- 

ing, legal advice, litigation, condemnation, damages, time of con 
struction, interest during construction, cost of structures and 
works, overhead costs, cost of financing, sinking fund, payments, 
interest, colonization, estimated time required, cost of develop 
ment, interest, maintenance, depreciation and operation, esti- 
mated return and new profits from venture. 

IX. Final Conclusions. 

27. Comparative data from other projects. 

28. Recommendations. 




Fig. 349. — Power House and Dam Abandoned Because Possible Power Output 
was not Sufficient to.jPay for Operating. 

268. Water Power. — The flow of streams is perennial. Coal, oil 
and gas are exhaustible. If the power of a flowing stream is developed 
for useful purposes, the country is richer, for something which other- 
wise would have been lost is saved and utilized ; and in general such 
saving' has also resulted in conserving an equivalent of fuel for the 
future which would have been lost. Water power is therefore an im- 
portant application of hydrology which demands greater consideration 
than it has received as yet. 



Water Power. 



613 



Agitation for so-called "conservation" has served to call attention to 
the desirability of the intelligent use of natural resources but has re- 
sulted in ill considered laws (1919) which have prevented development 
of water powers and resulted in a corresponding unnecessary use of 
exhaustible fuel resources. 

Intelligently developed, water powers are not only profitable to their 
promoters but from the very fact of their success show that they fulfill 
a demand which results in profit to their customers and a saving in the 
exhaustible natural resources and a development of the country. 

Water powers are not universally profitable. While the energy of 
running streams is a waste which a water power development is de- 
signed to prevent and to utilize, the expense of development is fre- 




Numbers represent percentages. 
Total represented S4,00O,OOO HP 



Fig. 350. — Percentage of Total Water Power in the United States Available 

in Each State. 

quently so great as to be unwarranted by the economy effected by the 
saving. Fig. 349 shows a 50 foot dam with power house which, while 
built in good faith, was so ill advised that it did not pay to operate it 
even after it was constructed and the investment incurred. The ma- 
chinery was removed through the opening in the power house wall and 
was installed on a larger stream. Many similar failures show the 
necessity of the consideration of all of the factors which when com- 
bined control the success of such projects. 

In water power projects, water is an essential feature, and the reg- 
ularity and quality of flow are important factors to investigate. (See 
Chapter XVI, p. 432). Head, however, is equally important and needs 



614 Application of Hydrology. 

full investigation as at times of flood, head is often reduced and is es- 
sentially eliminated in many low head plants. 

The creation of head by the construction of dams requires an in- 
vestigation of the geological conditions which are favorable or un- 
favorable to safe and economical storage of potential energies above a 
given site, and the intelligent construction of works to control and 
utilize the same. 

Storage and pondage are also vital factors in water power utilization. 
In no case can water power be utilized at a continuous uniform load, 
and much power will be lost at times of low demands unless the water 
can be impounded at such times and utilized during the time of high 
demand. A comparative study of load factor, load demand, stream 
variation and storage possibilities is therefore often as important as 
qualitative studies of available stream flow. 

The distribution of the approximate 54,000,000 horse power of 
water available in the United States is shown in Fig. 350. Of this 
only about 5.000,000 horse power were developed in 19 12 so that water 
power projects affords a great field for engineering work. 

269. Outline of Factors for Water Power Investigation. — 

I. Market or Demand for Power (proximity, nature and extent of market). 

1. Special use, particular industry, general, wholesale or retail sale 

of power, character of load, load factor, power factor, seasonal 
loading. 

II. Physical Conditions. 

2. Location: A topography, B geology, C climate, D rainfall (annual 

seasonal, variation), E temperatures (ice conditions), F fre- 
quency and character of storms (high winds, lighting) G earth- 
quakes. 

III. Hydrographic and Topographic Surveys. 

3. Streamflow (annual, monthly, daily, gagings and records). 

4. Plowage, storage and pondage (desirability, feasibility, effect). 

5. Canals (location, excavation, construction, seepage, etc.). 

6. Riparian lands, structure sites, railroads, transmission and tele- 

phone lines. 

7. Head (amount and variation under high, low and medium flows). 

8. Power (amount available, variations, amount desirable to develop, 

load factor). 

9. Auxiliary power (necessity, probable amount, source, fuel cost, etc., 

effect on cost of delivered power). 

10. Ultimate capacity and provisions for future growth of development. 

IV. Water Power Laws. 

11. Water rights, flowage rights, condemnation, privileges, damages, 

litigation. 



Water Power. 6 1 5 

V. Development. 

12. Land: A site, B flowage, C rights of way, D roads, E bridges. 

13. Dam: A foundations, B flood capacity, C spillway, D locks, E gates, 
F sluices, G fishways and logways. 

14. Headrace: A capacities, B loss of head, C headgates, D canal, 

E tunnels, F soil, G erosion, H silt, I lining, J grade, K racks, 
L gates, M penstock (open, closed). 

15. Power house and substations: A foundations, B type, (fireproof, 

wood, iron), C design (windows, doors, roof, floors, walls, gal- 
leries, rooms, stairways, heating, plumbing, water supply). 

16. Tailrace: A capacity, B permanency, C loss of head, D soil and 

material, E lining, F silt. 

17. Equipment: A turbines, B generators, C governors, D exciters. 

E switchboard, F lightning arresters, G transformers, H regula- 
tors, I oil purification, J gate operating machinery, K cranes. 

18. Transmission: A line losses (distance, voltage, transformation, 

amount of power), B conductors (material, insulation, stringing 
and sagging, ground wires), C type (wood pole, steel pole, steel 
towers, durability, foundations, painting, galvanizing). 

VI. Labor and Material. 

19. Work done by contract or force account: A labor (nationality, 

availability), B teams, C construction plant, D cost. 

20. Material: A sources, B transportation, C distance, D cost. 

21. Machinery for construction purposes: A kind, B availability, C cost. 

VII. Cost Estimate. 

22. Water rights, real estate, flowage, rights of way, promotion, ad- 

ministration, engineering and legal expenses, time of construc- 
tion, interest during construction, cost of construction and over- 
head, cost of financing, interest, discounts, sinking fund, pay- 
ments, maintenance, depreciation, operation, taxes, cost of power, 
load, load factors, cost compared with power costs of plants used 
or which may be used in territory, cost of development of market, 
contingencies of construction, development and operation, dam- 
ages, benefits, returns, profits. 

VIII. Financing. 

23. Common stock, preferred stock, bonds, securities, market, discount. 

IX. General Conclusions. 

24. Comparison with data from other developments, adequacy of works, 

conclusions, recommendations. 

270. Internal Navigation. — In the early development of a country 
the navigation of the interior waters may be of the utmost importance 
as the only practicable method of transportation. With the growth of 
the country and the increase in importance of rapid communication and 
transportation, railways have largely displaced waterways in importance 
and in most countries waterways have assumed a second and very sub- 



616 



Application of Hydrology. 




Internal Navigation. 617 

ordinate place. In the United States their practical importance has in 
many cases departed. 

In Fig. 351 are shown the navigable waters of the United States. 
There are about 25,000 miles of rivers in the United States that are now 
navigable for boats of various drafts and perhaps a further equal mile- 
age which can be made navigable. The Great Lakes are about 1,400 
miles in length but furnish a much greater length of navigable waters. 
There are also about 2,100 miles of canals in the United States part of 
which are however not navigable in part at the present time. 

The American canal at the Sault St. Marie carries more traffic than 
any other waterway of equal length in the world. This is because it 
controls the line of transportation from the iron mines of Minnesota, 
Wisconsin and Michigan to the furnaces along Lakes Erie and Michi- 
gan and of Ohio, Pennsylvania and Illinois. The great traffic over 
this short canal is unusual, as noted, and cannot fairly be used as an 
argument in favor of improving waters along lines on which no natural 
demand for navigation transportation exists. 

With further development and a growing demand for cheap trans- 
portation of bulky commodities, it is not inconceivable that the im- 
portance of internal waterways may increase in the future, but that 
they will, in the United States, ever again even approximate the im- 
portance of railways is hardly conceivable. What the future may de- 
velop with growth in population and increase in the cost and value of 
fuel and in labor difficulties can only be surmised. 

In late years there has been an attempt to arouse public interest and 
to create a public sentiment favorable to an immediate development of 
interior waterways. The more general, development and utilization 
of internal waterways in Europe has been used as an argument in favor 
of the general development of waterways in this country. It is im- 
portant to note, however, that there are already available in the United 
States more miles of navigable waters than in England, France, Bel- 
gium and Germany combined (see Table 65) and that the desirability 
of development of these resources in this country is purely a question 
to be determined from our own conditions. In the investigation of 
such problems their economic bearing should be determined as with 
all other problems, and no scheme for development should be advocated 
or adopted unless it can clearly be shown that its importance to the 
country will warrant the expense involved in construction, operation 
and maintenance. 



618 Application of Hydrology. 



TABLE 65. 

Relative Length in Miles of Waterways and Railways in Various Countries of 
Europe and in the United States in 1905. 

Canalized Total Total 

Rivers River Canals Waterways Railroads 

England and Wales 812 1,312 1,927 4,053 

France 796 970 1,777 7,485 2,445 

Belgium 75 307 334 1,016 2,873 

Germany 1,948 425 895 6,200 33,730 

United States 26,400 1,410* 2,190 30,010 222,571 

271. Outline of Factors of Navigation — Rivers, Canals and Har- 
bors. — 

I. General. 

I. Necessity, desirability, feasibility, benefits, tonnage carried or esti- 

mated, competition. 

II. Physical. 

2. Location: A topography, B geology, C climate, D rainfall variations 

and extremes, E temperature (ice, anvigation season), F storms, 
G earthquakes. 

III. Water Supply. 

3. Streamflow: (gagings, records, storage, equalization of flow, varia- 

tion of flow). 

IV. Water and Navigation Laws. 

4. Riparian rights: A rights of way, B condemnation, C litigation, 

D benefits and damages. 

V. Development. 

5. Surveys, hydrographic: A gagings, B soundings. 

6. Surveys, topographic and land : A rights of way, B sites, C canal and 

channel locations, D flowage. 

7. Dams: A foundations, B storage, C regulation, D wing dams. 

8. Harbors, wharfs, jetties, piers, lights, channel marks, warehouses. 

9. Locks: A size of vessels, B lift capacity, C gates, D time of operat- 

ing, E lock operating machinery. 
10. Equipment: A towing equipment, B lighting, C power (transmis- 
sion, cost), D loading and unloading machinery. 

II. Channels: A excavating, B dredging, C class of machinery. 

VI. Labor and Material. 

12. Method: A contract, B force account. 

13. Labor: A nationality, B availability. 

14. Material: A sources, B availability, C transportation, D distance, 

E cost. 

15. Construction plant and equipment: A nature, B cost. 

VII. Cost Estimates. 

16. Promotion, administration, engineering, legal, time of construction, 

interest during construction, construction and overhead costs, 
financing, appropriations, bonds, discounts, interest, sinking fund. 



*Great Lakes. 



sewerage. 



619 



damages, benefits, tolls, maintenance, depreciation, operation, 
taxes, contingencies. 

VIII. Financing. 

17. Appropriation, stocks, bonds, securities, market values. 

IX. General Conclusions. 

18. Comparisons, discussion, financial returns, recommendations. 
272. The Sewerage of Cities. — Of projects for the control of water 

those for the drainage and sewerage of cities are perhaps the most 
common and of the most general importance. 

The overflow of storm waters, even for brief periods, may be highly 
objectionable in a village and not at all permissable in cities or large 
communities, while such occurrence in the country though undesirable 
may not be of sufficient importance to warrant an expensive remedy. 
In the country, or even in the village community, the vault or cess pool 
while objectionable may temporarily serve the purpose of disposal of 
household waste. In cities, with public water supplies, the waste waters 
are increased in quantities and if cess pools are used they would soon 
saturate the soil with filth and create unhealthful conditions. Sewers 
therefore become essential for the conveyance of such wastes to points 
where they may be discharged without serious consequences or where 
they may be treated and their injurious characteristics removed before 
they are discharged into surface waters. 

273. Outline of Factors of Sewerage Projects. — 

I. Purpose. 

1. Uses and necessities of system, sanitation and removal by water 

carriage of domestic and industrial waste and storm water. 

II. Source and Amount of Sewage. 

2. Domestic: A quantity, B population present and prospective, 

C amount of water supply, D probable infiltration from ground 
water. . 

3. Industrial wastes: A quantity, B character of industry (dye works, 

tanneries, etc.). 

4. Storm water: A quantity, B rainfall, C drainage area, D character, 

E records and gagings, F comparisons with similar places, G run- 
off formulas. 

III. System. 

5. Gravity flow, pumping (source of power, cost). 

6. Sewers: A conduits (concrete, masonry, clay, metal), B capacity, 

C grade, D outfalls, E intercepting, F overflow. 

7. Accessories: A manholes, B catch basins, C lamp holes, D vents, 

E traps, F pumps and ejectors, G plumbing. 

8. Plant, A treatment (clarification, purification), B pumping. 

IV. Disposal. 

9. Dilution in stream: A stream flow (records and gaging). 



620 



Application of Hydrology. 



10. Broad irrigation. 

11. Settling and screening. 

12. Treatment: A septic, B filtration (sprinkling and contact niters) 

(activated sludge, D chemical reduction (trade waste), E sterli- 
zation. 

13. Sludge: A incineration, B fertilizer. 
V. Ownership and Management. 

14. Usually municipal ownership. 




Fig. 352. — Swamp Lands of the United. States. 

VI. Cost Estimates. 

15. Promotion, administration, engineering, supervision, legal expenses, 
time of construction, interest during construction, cost of con- 
struction and overhead, cost of financing, bonds, discount, inter- 
est, sinking fund, damages, benefits, maintenance, depreciation, 
operation, contingencies. 

VII. Financial. 

1G. Tax roll, special assessment, assessed valuation, bond limit, inter- 
est, maintenance, depreciation. 

VIII. General Conclusions. 

17. Comparisons, discussion, recommendations. 
274. Drainage. — For successful agriculture too much water is 
quite as detrimental as too little. There are many lands throughout 
the world that are too wet, periodically overflowed or permanent swamp 



D 



rainage. 



62 



which cannot be used for agricultural purposes to advantage if at all 
under the present conditions. The description of swamp and wet lands 
in the United States is given in Tab 1 e 66, and the swamp areas in the 
United States east of the Rocky Mountains are shown graphically in 
Fig"- 35 2 - 

TABLE 66. 

Swamp and Wet Lands of the United States. 



STATE 



Alabama 

Arkansas 

Cailfornia 

Connecticut . . . 

Delaware 

Florida 

Georgia 

Illinois 

Indiana 

Iowa 

Kansas 

Kentucky 

Louisiana 

Maryland 

Maine 

Massachusetts . 

Michigan 

Minnesota 

Mississippi .... 

Missouri 

Nebraska 

New Hampshire 
New Jersey .... 

New York 

North Carolina 
North Dakota . 

Ohio 

Oklahoma 

Oregon 

Pennsylvania . . 
Rhode Island . . 
South Carolina 
South Dakota . . 

Tennessee 

Texas 

Vermont 

Virginia 

Washington . . . 
West Virginia . 
Wisconsin 



Total 



Permanent 

Swamp 

Acres 



900,000 
5,200,000 
1,000,000 



50,000 

18,000,000 

1,000,000 

25,000 

15,000 

300,000 



Wet 
Grazing 

Land 
Acres 



59,200 
50,000 
[,000,000 
10,000 
50,000 



9,000,000 

100,000 

156,520 

20,000 

2,000,000 

3,048,000 

3,000,000 

1,000,000 



500,000 
100,000 
200,000 
59,380 
100,000 
1,196,605 



5,000 

326,400 

100,000 

1,000,000 

50,000 



254,000 



1,500,000 

100,000 

639,600 

1,240,000 

15,000 

600,000 

20,500 



947,435 

2,000,000 



100.00C 



100,000 

500,000 

50,00C 



1,000,000 



,000,000 



52,665,020 



6,826,019 



Periodically 
Overflowed 
Acres 



520,000 

531,000 

1,420,000 

20,000 

27,000 

1,000,000 

1,000,000 

400,000 

500,000 

350,000 

300,000 

300,000 



92,000 
39,500 



2,760,200 

1,439,700 

412,100 

7,700 



329,100 
500,000 

50,000 
100,000 

31,500 



50,000 

6,000 

622,120 

511,480 



8,000 
200,000 



23,900 



14,747,805 



Periodic- 
ally 
Swamp 
Acre 5 ! 



131,300 



200 
800,000 
700,000 



10,000 
80,500 

44,600 



784,308 



748,160 
50,000 
55,047 



2,064 
1,000,000 



!60,000 



1,766,179 



Total 

Acres 

1,479,200 

5,912,300 

3,420,000 

30,000 

127,200 

19,800,000 

2,700,000 

925,000 

625,000 

930,500 

359,380 

444,600 

10,196,605 

192,000 

156,520 

59,500 

2,947,439 

5,832,308 

5,760,200 

2,439,700 

512,100 

12,700 

326,400 

529,100 

2,748,160 

200,000 

155,047 

31,500 

254,000 

50,000 

8,064 

3,122,120 

611,480 

639,600 

2,240,000 

23,000 

800,000 

20,500 

23,900 

2,360,000 

79,005,023 



Drainage engineering varies in character from the simplest construc- 
tion of a tile drain or open ditch from a single farm to the most exten- 



622 Application of Hydrology. 

sive projects involving perhaps, as in the case of the Florida Everglades, 
the drainage of thousands of acres by the construction of large canals. 
Such projects sometimes entail the diversion of head waters from the 
land to be drained and the construction of dams and levees to prevent 
the inroad of the sea or the overflow of rivers which adjoin the lands 
to be reclaimed, protected or improved. 

The irrigation of extensive areas of land commonly involve the neces- 
sity of the drainage of the lower lands which are injured by seepage 
from the ditches and higher irrigated areas. This is commonly the re- 
sult of over-irrigation and can be modified and minimized but not 
wholly prevented by the intelligent use of irrigation water. The ex- 
tent of the injury to the lands of the U. S. Reclamatation Service (in 
1916) from this cause is shown in Table 67. 

TABLE 67. 

United States Reclamation Projects Estimates of Seepage and Summary of 

Drainage Work to June 30, 1911. 









rt a 


5 k 2 °fi.'A 

0> C C +J nj !■•■<-> 








Sh * 


hO- | " O « 




DRAINS 




<V£ Igfeg . 














Open 


Closed 


mat 

ecte 

cted 

ac 

rote 
)rair 
are 
ed 




miles 


miles 


*5 


^?2 


■SflbH 








6,400 

s.ooc 










1 


Arizona-California: Yuma .... 


14.5 


4.0 


12,000 52,000 


Colorado: 










Grand Valley 


.7 




250 
16,000 


5C 




1 


Idaho: 










Boise — 












Pioneer Irrig. Dst 


78.5 


.8 


10,500 


30,000 


30,000 


Nampa-Meridian Dst 


43.7 




6,200 


50,000 


50,000 


Other parts of project 


9.7 




2,050 


3,500 


3,500 


Minodoka 


100.0 




543 


30,000 


30,000 


Montana: 












Flathead (Indian) 


.18 


2.97 


360 


1,240 


1,240 
24,000 


Huntley 


15.77 


43.29 


1,704 


20,000 


Sun River 






2,250 


1 




Montana-North Dakota: 








Lower Yellowstone 


4.5 


1.1 


1,300 


1,600 


1,600 


Nebraska-Wyoming: 












North Platte 


20 4 


14 


3,000 


5 000 


6,000 
16,000 


Nevada: Truckee-Carson 


9.5 


3.99 


11,000 


11,000 


New Mexico: Carlsbad 


9.0 


3.9 


3,061 


2,769 


5,000 


New Mexico-Texas: Rio Grande. 


11.5 




55,000 


5,100 




Oregon : 






I 


, 




Klamath 


67 7 


5 7 


6,200 
9 00 


17,000 
2,000 

14,000 


29,600 

9 000 


Umatilla 


10 




South Dakota: Belle Fourche... 






3,250 
5,000 

I 




Wyoming: Shoshone 


11 57 


67 90 










17,500 



Drainage. 623 

275. Outline of Factors of Land Drainage Projects. — 

I. Physical. 

1. Location: A topography, B geology, C hydrological conditions, D 

climate, E rainfall and variations, F temperature, G transporta- 
tion (roads, railroads), H markets. 

II. Land. 

2. Area of District, area to be drained, soil and subsoil, fertility, ne- 

cessity for fertilizer, cultivation, vegetation, timber. 

3. Drainage: A necessity, B feasibility, C increase in productivity, 

D improvement in health conditions, E value. 

4. Ownership, legal rights. 

5. Drainage laws: A drainage district organization, B assessments 

(damages and benefits). 

III. Hydrology. 

6. Source of water (from district to be drained, from country draining 

into district, from flood overflow, from tide overflow). 

7. Surface water: A flow of streams (records, etc.), B drainage area 

(swamp, bayous), C storage, D rainfall, E diversion of streams, 
F topography. 

8. Ground water: A disposal, B works needed (open ditches, under- 

drains, levees, floodways, outlets, pumping plant). 

IV. Development Works. 

9. Surveys: A methods, B lines run, C natural drainage channels, 

D ditch locations, E rights of way, F profiles, G maps, H outlets, 
mensions and foundation, C soil. 

10. Intercepting and diverting levees and channels: A capacity, B di- 

mensions and foundation, C soil. 

11. Storage and flow retarding basins and channels. 

12. Levees: A stripping, B stratification and nature of subsoil, C muck 

ditches, D borrow pits. 

13. Channels and floodways: A size, B berms, C slopes, D construction, 

E protection (paving, mats). 

14. Ditches and drains: A capacities, B spacing, C depth, D length, 

E grade and protections, F character of soil. 

15. Bridges, roadways, culverts, weirs and drops. 

16. Pumping equipment: A location and capacity, B character of fuel, 

C cost. 

17. Outlets: A permanency, B protection, C gates (tide gates, etc.) 

D foundations, E consideration of effect on adjacent or contigu- 
ous areas. 

V. Construction. 

18. Under contract or force account. 

19. Labor: A nationality, B teams, C availability, D cost. 

20. Material: A sources, B distance, C transportation, D cost delivered. 

21. Machinery: A dredges (floating and caterpillar type dipper, clam 

shall, suction, dragline), B scraper (wheel, drag). 



624 Application of Hydrology. 

VI. Cost Estimates. 

22. Cost of Promotion, administration, engineering, supervision, legal 

expenses, time required for construction, interest during con- 
struction, cost of construction and overhead, cost of financing, 
bonds, discount, sinking fund, payments, interest, assessment of 
benefits and damages, cost of maintenance, depreciation, opera- 
tion, contingencies, taxes, estimated returns and profits. 

VII. General Conclusions. 

23. Comparative data from similar developments, adequacy of works. 

conclusions, recommendations. 

276. Flood Protection. — Flood protection works are frequently a 
part of the works for the drainage of cities and agricultural lands. 
With the growth of settlements, of homes, farms and manufacturing 
establishments on the flood plains of rivers, the event of even occa- 
sional overflows becomes too serious to be permitted to continue. As 
a consequence some of the most important engineering undertakings 
are included under this subject and demand not only a most profound 
study of the hydrology of floods but also the design and construction 
of the most economical works for their control. 

277. Outline of Factors for Flood Protection Investigation. — 

I. Physical Conditions. 

1. Location: A topography, B geology, C area to be protected, D drain 

age area producing floods, E climate, F rainfall, G temperature, 
H hydrological conditions, I relation of area to flood plains and 
flood heights. 

II. Land and Property. 

2. Character: urban, residential, industrial, rural, agricultural. 

3. Land: amount, character, productiveness, value. 

4. Effect of floods: A protection (necessity, desirability, feasibility), 

B value of lines and property involved. 

III. Floods. 

5. Flow of streams: A gagings (magnitude and frequency of flood 

heights, records), B drainage area (characteristics, topography*. 
C rainfall. 

6. Channel storage, stream congestion. 

IV. Laws. 

7. District organization : A legality, B rights, C damages and benefits. 

D litigation. 

V. Development. 

8. Surveys: A topography, B channel and levee locations, C rights of 

way, D change in railroads, roads, pole lines, etc. 

9. Works needed: A confining, B controlling, C intercepting, D divert- 

ing, E impounding and flow retarding works, F capacities. 

10. Dams (foundations, outlets, spillways). 

11. Levees and channels: A height, depth, capacity, grades, B erosion. 

C revetments and protection, D currents and waves. 



Flood Protection. 625 

12. River training: A revetments, B pavements, C jetties, D wing dams. 

13. Bridges (roadways, railways). 

VI. Construction Methods. 

14. Contracts, force account. 

17. Labor: A nationality, B availability, C teams, D cost. 

18. Camp requirements. 

19. Material: A sources, B distance, C transportation, D cost. 

20. Machinery, type and class available for economic construction. 

VII. Cost Estimates. 

21. Cost of promotion, administration, engineering supervision, legal 

expenses, time of construction, interest during construction, con- 
struction camp, original cost and maintenance, construction costs, 
financing, bonds, discounts, interest, assessment, benefits and 
damages, maintenance, depreciation, operation contingencies. 

VIII. General Conclusions. 

22. Comparative data, adequacy of works, discussion, recommendations. 

LITERATURE 

PUBLIC WATER SUPPLIES 

Public Water Supplies, Turneaure and Russell, John Wiley and Sons, Inc., 
New York. 

Waterworks Handbook, Flinn, Weston and Bogert, McGraw-Hill Book Co., Inc., 
New York. 

Water Supply Engineering, A. ,P. Folwell, John Wiley and Sons, Inc. New York. 

Water Supply — Considered Principally from a Sanitary Standpoint, W. P. Ma- 
son, John Wiley and Sons, Inc., New York. 

The Filtration of Public Water Supplies, Allen Hazen, John Wiley and Sons, 
Inc., New York. 

Water Purification, J. W. Ellms, McGraw-Hill Book Co., Inc., New York. 

Water^ — Its Purification and Use in the Industries, W. W. Christie, D. Van 
Nostrand Co., New York. 

The Microscopy of Drinking Water, G. C. Whipple, John Wiley and Sons, Inc., 
New York. 

IRRIGATION 

Irrigation Engineering, Davis and Wilson, John Wiley and Sons, Inc., New 

York. 
Irrigation Practice and Engineering (3 vol.), B. A. Etcheveny, McGraw-Hill 

Book Co., Inc., New York. 
United States Irrigation Works, A. P. Davis, John Wiley and Sons, Inc., New 

York. 
Use of Water in Irrigation, S. Fortier, McGraw-Hill Book Co., Inc., New York. 
Irrigation Pocket Book, R. B. Buckley, Spon and Chamberlain, New York. 
Principles of Irrigation Engineering, Newell & Murphy , McGraw-Hill Book Co., 

Inc., New York. 
Operation and Maintenance of Irrigation Systems, S. T. Harding, McGraw-Hill 

Book Co., Inc., New York. 



626 Application of Hydrology. 

, WATER POWER 

Water Power Engineering. D. W. Mead, McGraw-Hill Book Co., Inc., New York. 
Hydro Electric Power Stations, Loe and Rushmore, John Wiley and Sons, Inc., 

New York. 
American Hydroelectric Practice, Taylor and Braymer, McGraw-Hill Book Co., 

Inc., New York. 

NAVIGATION 

The Regulation of Rivers, J. L. Van Ornum, McGraw-Hill Book Co., Inc., New 

York. 
Improvement of Rivers (2 vols.), Thomas and Watt, John Wiley and Sons, 

Inc., New York. 
Rivers and Canals (2 vols.), L. F. Vernon-Harcourt, The Clarendon Press, 

Oxford, England. 
Coast Erosion and Protection. Ernest R. Matthews, Charles Griffin and Co., 

Ltd., London. 
Harbour Engineering, Brysson Cunningham, Charles Griffin and Co., Ltd., 

London. 
Tidal Rivers, W. H. Wheeler, Longman, Green and Co., New York. 

SEWERAGE 

American Sewerage Practice (3 vols.), Metcalf and Eddy, McGraw-Hill Book 

Co., Inc., New York. 
Sewerage. A. P. Folwell, John Wiley and Sons, Inc., New York. 
Sewer Design, H. W. Ogden, John Wiley and Sons, Inc., New York. 
Sewage Disposal, Kinnicutt, Winslow and Pratt, John Wiley and Sons, Inc., 

New York. 
Seivage Disposal, G. W. Fuller, McGraw-Hill Book Co., Inc., New York. 

DRAINAGE 

Engineering for Land Drainage. C. G. Elliott, John Wiley and Sons, Inc., New 

York. 
Professional Papers and Reports on Drainage. Office Experiment Station, U. S. 

Dept. Agriculture, Washington, D. C. 

FLOOD PROTECTION 

Relief from Floods, Alvord and Burdick, McGraw-Hill Book Co., Inc., New 

York. 
Reports Miami Conservancy District, Dayton, Ohio. 
See also Literature Chapter XIX, p. 594. 

GENERAL 

The Control of Water, P. A. M. Parker, D. Van Nostrand Co,. New York. 
Reservoirs for Irrigation. Water Power and Water Supply, J. D. Schuyler, 

John Wiley and Sons, Inc., New York. 
Hydraulic and Water Supply Engineering, J. T. Fanning, D. Van Nostrand Co., 

New York. 
Treatise on Hydraulic. Hughes and Safford, Macmillan Co., New York. 
Hydraulics and its Applications. A. H. Gibson, D. Van Nostrand Co., New York. 
River Discharge, Hoyt and Grover, John Wiley and Sons, New York. 



Abbe, Cleveland, evaporation factors. 

148. 
Adirondack Region, 362. 
Advective Region, 46. 
Agriculture, 

control of water for, 38. 
flood plain, 39. 

seasonal divisions of year, 236. 
water supply for, 37. 
water necessary for, 25. 
Airy, Prof. G. B., waves, 180. 
Alexandria, La., intense rainfall, 279. 
Algonkian Rock, 356. 
Alkali Salt, western ground water, 

414. 
Alkali, irrigation project, 608. 
Altapass, N. C, 

intense rainfall, 247, 302. 
rainfall, 176. 

see Precipitation, Altitude. 
Altitude, 

atmospheric moisture, 114. 
atmospheric temperature, 114. 
boiling point, 133. 
evaporation, effect, 126, 133, 

135. 
maximum precipitation, 168. 
precipitation, effect, 167. 
precipitation data, 16S. 
Amazon, R., bore, 94. 
American Rainfall Records, 13. 
Appalachian region, 

geology, 362, 367. 
rainfall, 284. 
Applied hydrology, 597, 598. 

literature, 626. 
Archean rocks, 353, 356. 

outcrop, 373. 
Arizona, rainfall, 295, 307. 
Arkansas, 

drainage runoff, 585. 
Silurian period, 367. 
Artesian, 

areas in U. S., 405. 



Artesian — Continued — 

Barton Spring, Texas, 401. 
cause, 399, 404. 
drift, 405. 

East Minneapolis, 363. 
flow variations, 405. 
head, 383. 
head, 383. 

origin of word, 404. 
Artesian Wells, see wells. 
Ashtabula River, 

comparative drainage areas, 

525. 
comparative hydrographs, 525. 
estimated flow, 534. 
geological conditions, 527. 
hydrographs, 527. 
mass curves, 526. 
rainfall, 528. 
rainfall-runoff, 532. 
reservoir capacity, 525. 
runoff estimates, 527. 
Assumption, errors in, 17. 
Atlantic Coast, changes in, 346. 
Atlantic Plain, artesian section, 405. 
Atmospheric circulation, see circula 

tion, atmospheric. 
Atmosphere, 

composition, 46. 
depth of, 45. 
envelope of earth, 44. 
influences, 45, 46. 
isothermal region, 45. 
Atmospheric moisture, see moisture, 

atmospheric. 
Atmospheric pressure, see pressure, 

atmospheric. 
Atmospheric temperatures, see tem- 
perature. 
Austin, Texas, 

borings, 388. 

dam, 6, 402. 

silting lake, 342. 

stream flow extremes, 434. 



628 



Ind 



ex- 



Austria, rainfall and altitude, 300. 
Avalanch, 318. 

Babb, C. C, 

sediment in rivers, 324. 

runoff estimate, 502. 
Backwater , effect on flow, 482. 
Baker, F. S., evaporation, 137. 
Barometric Pressure, see pressure 

atmospheric. 
Base level, 381. 

Bay of Fundy, tide height, 93. 
Bennett, S. G., rainfall runoff rela- 
tions, 500. 
Bias, effect of, 14. 

Biglow, F. H., evaporation measure- 
ment, 133, 151. 
Binnie, A. A., precipitation varia- 
tions, 215. 
Black River, 

dam failure, 332. 

flood 1911-7, 555. 

preglacial, 332. 
Blanford, H. F., precipitation in 

India, 160. 
Boiling Point, reduction with alti- 
tude, 133. 
Bore, Amazon River, 94. 

Hancow, China, 94. 
Borings, Austin, Tex., 388. 

Hales Bar Dam, 387. 
Boston, precipitation expectancy, 219. 
Boulders, rapids, 333. 
Bristol Channel, tide heights, 94. 
Bruckner, vapor interchanges, 123. 
Buffalo, N. Y., wind tides, 99. 

California, artesian section, 405. 

precipation, 160. 

rainfall, 291. 

rainfall-runoff relations, 500. 
California, Gulf of, tide heights, 94. 
Cambrian Period, 362. 
Cambridge, Ohio, intense rainfall, 245. 
Canals, feasibility of, 25. 

navigation, 617. 
Carboniferous Period, 368. 
Casualties, lack of knowledge, 5. 
Catskills, rainfall, 290. 
Cause and effect, 17. 



Caves, 371. 

Chamberlain, Prof. T. C, 

artesian conditions, 404. 

Potsdam Sandstone, 363. 
Channel, 

shifting effect of flow, 482. 

flow in uniform, 480. 

restrictions, 572. 
Chief of weather bureau, report of 

172. 
China, flood losses, 550. 
Chittenden, General, floods, 574. 
Cincinnati shale, 366. 
Circulation, Atmospheric, 

see also winds. 

cause, 51, 55. 
Circulation Atmospheric, 

Ferrels Law, 56. 

influencing factors, 55, 62. 

uniform planet, 58. 

velocities, 57. 
Circulation Lake, see lake currents. 
Circulation, ocean, 

see ocean currents. 
Circulation of water, 30, 31. 
City Areas, runoff from, 584, 586. 
Climatic changes, past ages, 212. 
Climatic Conditions, similarity, 13. 
Climatological Data, 172, 194. 
Cloud, altitude, 167. 
Coal measures, 368. 
Coast changes, see land. 
Coast, precipitation, 164. 
Cold waves, 81. . 

Colonization, irrigation project, 608. 
Colorado, artesian wells, 405. 
Colorado River (Texas), 

storage calculations, 522. 
Columbia River, flood frequency, 570. 
Commerce, by waterways, 25. 
Comparisons, climatic conditions, 18. 

hydrological conditions, 11. 
Complex phenomena, defined, 12, 17. 
Conclusions, based on experience, 10. 

danger of general, 17. 

precipitation data, 159. 
Condensation, dewpoint, 123. 

heat changes, 124. 
Conditions, physical, 598. 
Cone of depression, wells, 425, 428. 



Ind 



ex. 



629 



Conservation, water power, 613. 
Consideration, fundamental, 597. 
Contamination, water supply, 33. 
Continental shelf, 344. 
Control of water, 598. 
Convective, precipitation, 160. 
Cooling, dynamic, 125. 

earth's crust, 358. 
Coosa River, rainfall-runoff, 504. 
Corrasion, 310, 313. 
Cioton River, Vermuele's formula, 510. 
Cultivation, stream flow factor, 454. 
Culverts, capacity, 589. 

flood studies, 544. 
Cumulative, rainfall and runoff, 492. 
Cunningham, Brysson, waves, 106, 107. 
Current, Lake, see Lake currents. 
Current, Ocean, see Ocean currents. 
Curtis, G. E., precipitation, classifica- 
tion, 160, 163. 
Cycles of precipitation, 208, 212. 
Cyclone, intense rainfall, 250. 

origin, 166. 

precipitation, in, 161, 166, 167, 
176, 250. 
Cyclonic Storm, see winds, see storms. 

Dakota, 

artesian section, 405. 
Dam design, 333. 

failure, Austin, Tex., 6. 
Black River Falls, 332. 
Hatfield, 553. 
Stoney River, W. Va., 6. 

flood capacity, 593. 

flow measurement, 483. 
Danger of general conclusions, 17. 
Danube River, floods, 574. 
Darcy, D. H., ground water flow, 419. 
Data, intense rainfall, limitations, 245. 

precipitation, 157, 168. 

stream flow, 483. 

use of, 11. 
Deductive Reasoning, 15. 
Definition, Hydrology, 1. 
Delta, glacial, 377. 

growth of, 348. 

Mississippi, 386. 
Denver Irrigation Laboratory. 

soil evaporation, 143. 



Desert, atmospheric moisture, 121. 
due to trade winds, 59. 
precipitation, 33. 
Detritus, carried by stream, 314. 
Devonian Outcrop, extent of, 367. 
Devonian Period, 367. 
Dew, cause, 125. 
Dew point, 123. 

cloud formation, 166. 
defined, 114. 
occurrence, 167. 
Biastrophism, 317, 344. 
Dickenson and Evans, soil evapora- 
tion, 141. 
Dike, Kicking Horse River, 328. 
Dip of strata, 373. 
Discharge, River, see stream flow. 
Disposal of waste, 38. 
Doldrums, moisture, 121. 
Drainage areas, comparative, 525. 
determination of, 485. 
Great Lakes, 457. 
Peshtigo River, 538. 
storage, natural, 456. 
storage surface, 459. 
stream flow, 446, 444. 
water supply, maximum, 466. 
water supply, minimum, 469. 
water supply, variable, 468. 
Drainage Districts, flood runoff, 585, 

588. 
Drainage, effect on lands, 156. 

factors in investigation, 623. 
glacial, 379. 
importance, 620. 
irrigated land, 608, 622. 
literature, 626. 
origin of valleys, 325. 
post glacial, 378. 
preglacial, 373. 
swamp, 36, 39. 
storage, subsurface, 459. 
stream flow factor, 453. 
underground, 371. 
Drift, artesian conditions, 405. 
sections of, 380. 
water supply, 382. 
Driftless area, 371, 281. 
Duration Curves, Peshtigo River, 540. 
Dunwoody, thunder storms, 183. 



630 



Inde 



x- 



Liuryea, Edwin, evaporation, 133. 

Eagre, 94. 

Earth, crust irregularity, 28. 
crust movement, 317. 
crust wraping, 358, 371. 
envelopes, 44. 
surface area, 28. 
surface elevation, 28. 
surface, original, 43. 
surface, present, 44. 
temperature distribution, 51. 
Earthquake, Japan, 319. 
literature, 350. 
Mississippi Valley, 320. 
San Francisco, 320. 
East Indian Tyhoon, 78. 

see wind. 
Economics, considerations of, 598. 
flood protection, 592. 
stream control, 516. 
Effect and Cause, confusion in, 17. 
Effective size, soil grains, 420. 
Elliot, C. G., drainage district runoff, 

585. 
England, changes in coast, 347. 
Envelopes of earth, 44. 
Engineering, basis of, 4. 
conclusions, 18. 
design for extreme econditions, 

280. 
failures in, 20. 
fundamental principles, 478. 
geology, 352, 386. 
knowledge necessary, 4. 
precipitation, effect, 157. 
problems, 478. 
success and failure, 5. 
Erosion, effect on navigation, 38. 
effect on soils, 38. 
factors of, 310, 312. 
flood effects, 546. 
glacial, 316. 
results of, 324. 
vegetation effect, 456. 
wave action, 314. 
weathering, 312. 
Errors in assumption, 17. 
Estimates, rainfall, 13, 196. 
Europe, internal navigation, 617. 



Evaporimeter, 150, 151. 
Evaporation, 31. 

altitude effect, 133, 135. 
annual and rainfall, 15. 
annual in United States, 126. 
atmospheric moisture, source, 

163. 
calculation, 153. 
factors of, 126, 149. 
forest effects, 148, 455. 
formulas, 153. 
geology, effect, 309. 
heat changes, 124. 
knowledge, importance, 152. 
lakes and swamp, 457. 
land, see evaporation, soil, 
land surface, influences, 127. 
literature, 154. 
measurement, 150. 
occurrence, 123, 125. 
precipitation, 159, 164. 
Evaporation, soil, 391. 
experiments, 141. 
factors, 138, 143. 
rainfall relations, 141. 
snow and ice, 135. 
snow, forest effect, 138. 
storage, effect, 152. 
streamflow factor, 152, 448, 453, 

470. 
study, 127. 
surface waters, 35. 
temperature effect, 130. 
water surface, 12.5, 127. 
wind effect, 84, 132. 
vapor tension, effect, 127. 
variations, 126. 
vegetation, 144. 
Evolution, 43. 

Experience, basis of conclusions, 16. 
engineering practice, 4. 
value, 18. 
Exploration, settlement, 3. 

Factors, drainage project, 623. 

flood protection project, 624. 
hydrological considerations, 

597. 
internal navigation, 618. 
irrigation investigation, 609. 



Ind 



ex. 



63 



Factors — Continued — 

other than hydrological, 597. 
sewerage investigation, 619. 
water power investigation, 614. 
water supply, 603. 
Factor of Safety, engineering, 11, 478. 
evaporation estimates, 153. 
extreme conditions, 280. 
flood flows, 580. 
necessity for 593. 
rainfall estimates, 158. 
Failures, engineering work, 20. 
irrigation projects, 607. 
water power project, 613. 
Falls, origin, 327, 380. 
Fault, Austin, Tex., 402. 
Ferrel's Law, 56. 
Financial, economic considerations, 

598. 
Fitzgerald, Desmond, evaporation, 129, 

132, 133, 137. 
Flood, advance of wave, 563. 
Black River, 7, 557. 
cause of, 446, 558. 
channels, 544. 
channel restrictions, 572. 
design of structures, 593. 
disasters, 548. 
destruction by, 28. 
duration, 565. 
effects, 544. 
Erie, Pa., 466. 
factors in, 558. 

flow estimating, literature' 595. 
forest effects, 18, 572. 
formulas, 579. 
city areas, 586. 
comparison, 581. 
derivation, 591. 
drainage district, 588. 
frequencies, 569, 572. 
Galveston, Tex., 1900 and 1915, 

79. 
height increase, 571. 
importance of study, 544. 
increase, 570. 
intensity of, 579. 
intense rainfall, 266. 
Johnstown, Pa., 6. 
Kansas City, 6. 



Flood — Continued — ■ 

Kuichling formula, 583. 
levees, 464. 
levee damage, 593. 
literature, 594. 
losses, 548. 
maximum, 10. 
maximum rainfall, 274. 
Miami Valley, 1913, 7. 
Mississippi River, 550, 551. 
occurrence, 561. 
Passaic 1903, 6. 
protection, 41, 544. 
economics, 592. 
factors for investigation, 624. 
factors of safety, 593. 
importance, 624. 
literature, 626. 
value of, 546, 548. 
railway culverts, 589. 
rainfall effect, 566. 
retardation of wave, 494. 
rise, duration and recession, 

565. 
runoff, city areas, 584. 

drainage districts, 585. 
Sacramento River, 557. 
Stewart, C. B., 584. 
storage effect, 574. 
structures for, 544. 
topography, 353. 
under ground water, 36. 
United States, 557. 
utilization of flood plains, 41. 
wave progression, 563. 
Wisconsin, 553, 584. 
Florida Everglades, 
drainage, 622. 
freezing, 82. 

intense rainfall frequency, 249. 
runoff, 589. 
Flow of streams, see stream flow. 
Flow, porous medium, 418. 
Fogs, cause, 125. 
Forest, 

evaporation effect, 148, 455. 
evaporation from snow, 138. 
flood effects, 18, 572. 
precipitation effect, 169. 
rainfall, 18. 



632 



Ind 



ex- 



Forest — Continued — 

streamflow factor, 454, 470. 

streamflow literature, 471. 

transpiration, 148. 
Formulas, 

derivation, flood, 591. 

evaporation, 153. 

flood flow, 568, 579, 581. 

intense rainfall, 263. 

rainfall, 263. 

rainfall runoff, 502. 

runoff, city areas, 58G. 

runoff, drainage district, 588. 
Fortier, Dr. Samuel, evaporation, 130, 

133. 
Fossils, Cambrian, 362. 

carboniferous period, 368. 

Niagara limestone, 367. 

St. Peter sandstone, 366. 

Trenton limestone, 365. 
Foundations, geology, 387. 
P' ranee, rainfall and altitude, 306. 
Frances, Jas. B., intense rainfall, 244. 

flood, 569. 

intense rainfall, 244, 253. 
see also rainfall, intense-. 

Frequency, 

precipitation probabilities, 224. 
Frost, cause, 125. 
Fuller, W. E., floods and storage, 568, 

574. 
Fundamental Laws, 12. 
Funds, procuring, 597. 

Gage, recording, 480. 

Gaging station, 479, 482. 

Gaillard, Capt. D. D., waves, 106, 107. 

Galena limestone, 366. 

Galveston, Tex., 

storm, 7, 79. ■ 

Avind tides, 99. 
Geneva, N. Y., soil evaporation, 141. 
Geography, 

physiography, 13. 

streamflow factor, 444. 
Geological agencies, literature, 349. 
Geological changes, influence of 
water, 23. 



Geological conditions, local influence, 

18. 
Geological data, 14. 
Geological, time, 355. 
Geology, 

Ashtabula River, 527. 

Cambrian period, 362. 

Carboniferous period, 368. 

causes of changes, 310. 

changes in lands, 344. 

Cincinnati shale, 366. 

Devonian period, 367. 

disintegration of rock, 310. 

engineering, 352. 

faults, 402. 

floods, 353. 

historical, 354. 

Hudson River snale, 366. 

Huronian period, 358. 

hydrological influence, 309. 

hypothetical maps, 359. 

interior sea, Great Lake re- 
gion, 358. 

investigation, 387. 

Keweenawan period, 358. 

literature, 388 

Lower Magnesian limestone, 
365. 

map of United States, 356. 

Niagara limestone, 367. 

Ordovician period, 365. 

origin of falls and rapids, 327. 

origin of valleys, 325. 

outcrops in United States, 383. 

Potsdam formation, 362. 

Precambrian, 356. 

recent sedementary deposits, 
368. 

rock structure, 311. 

Silurian period, 367. 

storage of water, 352. 

St. Peter sandstone, 365, 366. 

strata characteristics, 369. 

strata modifications, 369. 

strata, order of, 355. 

factor, streamflow, 446. 

study of, 309, 352. 

Trenton limestone, 365, 366. 

upper Mississippi, 360. 

warping, 358. 



Ind 



ex. 



633 



Geology — Continued 

water bearing formations, 354. 
water supply, effect, 352. 
Germany, rainfall, 285. 
Gilbert and Lawes, soil evaporation, 

141. 
Glaciers, 31. 

active, 317. 
cause, 375. 
cause of motion, 377. 

drainage, 379. 

erosion by, 316, 373, 377. 

extent, 381. 

literature, 349. 

moraine, 377. 

period, cause of, 375. 
first, 378. 
second, 378. 

recession of, 378. 

river diversion, 450. 

topographical changes, 375, 381. 

work of, 331, 377. 
Gradient, flow of ground water, 422. 

ground water, 460. 

wells, effect, 425. 
Great Basin, 344. 
Great Lakes, drainage area, 457. 

geology, 360. 

navigation, 617. 

origin, 336. 

preglacial, 336. 

streamflow from, 457. 
Great Plains, precipitation, 166. 
Great Rainfall, see rainfall, intense. 
Greaves, Chas., soil evaporation, 111. 
Ground Water, artesian, 404. 

depth, 393. 

disposal of precipitation, 34. 
Ground water, floods in, 36. 

flow effective size, 420. 

flow experiments, 418. 

flow gradient, 422. 

flow, porosity, 420. 

flow temperature, 421. 

flow velocity, 416. 

gradient, 395, 408, 426, 460. 

head, 383. 

hydraulics of flow, 419. 

importance, 390. 

literature, 429. 



Ground Water — Continued — 

mineral content, 411. 

movement, 395. 

occurrence, 35, 390. 

origin, 390. 

pollution, 415. 

qualities, 411. 

quantity, 416. 

river underflow, 407. 

slides due to, 36. 

soil absorption, 393. 

stream flow, 390, 450, 460, 494. 

source of, 36, 390. 

supply from, 36. 

surface appearance, 398. 

temperature, 409. 

wells, 36, 423. 
Grunsky, C. E., evaporimeter, 151. 

runoff rule, 500. 
Guinea, Va., intense rainfall, 246. 
Gulf States, freezing, 82. 

Hales Bar Dam, borings, 387. 
Hancow, China, bore, 94. 
Harrington, M. W., forest, effect of 
evaporation, 148. 

transpiration, 147. 
Harza, L. F., flood probabilities, 570. 
Hazen, Allen, ground water flow, 419. 

precipitation expectancy, 225. 
Health, affect of water, 23. 

water supply consideration, 37. 
Heat, atmosphere absorption, 48. 

changes in evaporation, 124. 

latent, 124. 

soil absorption, 48. 

water absorption, 49. 
Henry, A. J., seasonal precipitation, 

237. 
Hertfordshire, England, soil evapora- 
tion, 141. 
Hill, S. B., storage calculations, 520. 
Himalayas, rainfall, 285. 
Hinrich, Gustavus, precipitation an- 
alyses, 237, 239. 
Historical Geology, 354. 
Hot Springs, cause, 411. 
Hot waves, cause of, 84. 
Hudson River shale, 366, 369. 



634 



Index- 



Humidity, absolute and relative, 112. 

variations, 122. 
Huronian period, 358. 
Hurricane, precipitation, 175, 249, 301, 

see wind. 
Hydrography, 89. 

literature, 42. 
Hydrographs, Ashtabula River, 527. 
comparative, 435, 515, 523, 535, 

537. 
comparative jPeshtigo River, 

537. 
comparisons, 435. 
study of, 474. 
value of, 515. 
Hydrological Conditions, 12. 
Hydrological Data, 11. 
Hydrological Estimates, 13. 
Hydrological Knowledge, 13. 
Hydrological Literature, study of, 20. 
Hydrological phenomena, variations, 

9. 
Hydrological Relations, determina- 
tion of, 14. 
Hydrology, application, 597. 
applied, 598. 
definition, 1. 
fundamental considerations, 

597. 
general, 1. 
industries, effect, 3. 
influence on early settlement, 3. 
laws of, 12. 

general, literature, 22, 42. 
natural laws, 2. 
necessity of study, 5, 42. 
problems and principles, 478. 
purpose of, 19. 
study of. 19. 
values, effect, 4. 
Hydrosphere, 44. 

Hydraulics, ground flow, 395, 418. 
Hydraulics, stream flow, 480. 

wells, 425. 
Hypothesis, formulation of, 15. 

truth of, 16. 
Hydraulic Engineering, failures, 5. 

i 

Ice bergs, 31, 317. 

Ice, effect of streamflow, 482. 



Ice — Continued 

evaporation, 135. 
storage effect, 491. 
transportation of detritus, 323. 
Illinois, artesian head, 383. 

Carboniferous period, 368. 
drift sections, 380. 
Hudson River shales, 369. 
Lower Magnesian limestone, 

365. 
Ordovician period, 365. 
Silurian period, 367. 
Impurities in water, 32. 
Indiana, Devonian period. 367. 
Indian Ocean, winds, 78. 
Inductive reasoning, 15. 
industry development, 3. 
Industry and water power, 27. 
Influences, complexity, 12. 
Interior Sea, Cambrian. 362. 

Great La"ke Region, 358. 
Internal navigation, 615. 
Introduction, 1. 

Investigation, drainage project, 623. 
flood protection project, 624. 
irrigation, 609. 
local conditions, 13. 
navigation proect, 618. 
sewerage project, 619. 
water power project, 614. 
water supply, 603. 
luwa, ground water quality, 413. 

Silurian period, 367. 
Irrigation, application, 604. 
colonization, 608. 
extent. 605. 

factors for investigation, 609. 
failures of, 607. 
Hondo project, 8. 
Italy and South Africa, 229. 
literature. 625. 
precipitation, seasonal, 237. 
profit from, 506. 
projects, failures, 8. 
projects in United States, 605. 
rainfall, 18. 
seepage, 465. 
use of water, 25. 
water supply, 408, 416, 476. 
Islands, precipitation, 164. 






Ind 



ex. 



635 



Isohyetals, intense rainfall, 266. 

rainfall map, 198. 
Isothermal region, 45. 
Isotherms, of earth, 51. 

Japan, earthquake, 319. 

Johnstown Flood. 6. 

Justin, J. D., runoff formula, 512. 

Karnes, 377. 

Kansas City flood, 6. 

Kansas, river underflow, 408. 

Kaw River, floods, 558. 

Kettle holes, 377. 

Keweenawan period, 358. 

Knowledge, casualties due to lack, 

hydrological limitations, 13. 

hydrological sources, 13. 

necessary for engineering, 5. 
Kuichling, flood formulas. 583. 

Lake Agassiz, 343, 378, 379. 
Lake Bonneville, 343. 
Lakes, classification, 335. 
currents, 

cause, 89. 

vertical, 90. 
Erie, wind tides, 98. 
Geneva, seiches, 100. 
glacial, 377, 378. 
Huron, seiches, 102. 
Lahontan, 343. 
literature, 111, 351. 
Michigan, 

glacial alteration, 378. 

preglacial, 373. 

seiches, 100. 
Minnesota, 379. 
origin, 335. 
Pepin, origin of, 338. 
permanency, 341. 
precipitation, effect, 166. 
rainfall, effect, 300. 
silting, 342. 
streamflow factor, 457. 
St. Croix, origin, 339. 
Superior, 

seiches, 100. 

wave pressure, 108. 
Landa. Ernst, flood in Danube, 574. 



Land, 

areas of earth's surface, 28. 

changes in extent, 344. 

protection from floods, 41. 

reclamation, 4. 
Landslide, 318, 320. 

literature, 350. 
Land Surface Evaporation, see evapor- 
ation. 
Latent Heat, 124. 
Laurentian Outcrops, 362. 
Laws, fundamental, 12. 

meteorological phenomena, 10. 

natural, 2, 12, 17. 
Levees, channel restriction, 572. 

effect, 465. 

flood, design for, 593. 

flood height eeffct, 572, 579. 

Mississippi R., 550. 
I ee Bridge, England, soil evaporation, 

141. 
Lee, Chas. L., evaporation, 137. 
Le Roy, N. Y., intense rainfall, 245. 
Life, necessity of water, 23. 
Lippincott, J. B., evaporation, 137. 

rainfall and altitlde, 307. 

rainfall-runoff relations, 500. 
Literature, altitude and rainfall, 307. 

applied hydrology, 626. 

drainage, 626. 

earthquake, 350. 

evaporation and atmospheric 
moisture, 154. 

floods, 594. 

flood flow estimating, 595. 

flood protection, 626. 

forest and streamflow, 471. 

general hydrology, 22. 

geological agencies, 349. 

geology, 388. 

glaciers, 349. 

ground water, 429. 

hydrography, 42. 

hydrological, study of, 20. 

hydrology, general, 42. 

irrigation, 625. 

lakes, 111. 

lakes, harbors, etc., 351. 

land slide, 350. 



636 



Ind 



ex- 



Literature — Continued — 

navigation, 626. 

ocean currents, 109. 

precipitation, 186, 226. 

precipitation measurement, 198. 

public water supply, 625. 

rainfall and altitude, 307. 

rainfall and streamnow, 470. 

rainfall intense, 280. 

rainfall-runoff, 543. 

rivers, 350. 

sewerage, 62G. 

streamnow literature, 471. 

streamnow variations, 508. 

storage and pondage, 543. 

tides, 109. 

transportation by streams, 350. 

water power, 626. 

waves, 110. 

wells, 430. 

winds and storms, 88. 
Lithosphere, 44. 
Local conditions, data applicable, 19. 

hydrological, 12. 

investigation, 13. 

similarity, 158. 
Logic., reasoning, 16. 
Los Angeles, Cal., intense rainfall, 

302. 
Louisiana, drainage district runoff, 
589. 

wind tides, 99. 
Lower Magnesian Limestone, 365. 

Madison, Wis., intense rainfall, 253, 
258, 279. 

precipitation expectancy, 217. 

precipitation maximum annual, 
212. 

precipitation monthly, 233. 

precipitation probability, 221. 

rainfall, 9. 
Mantle Rock, 354. 
Manufacture, water supply for, 37. 
Map, geological, N. America, 359. 

rainfall, 198. 

use of, 485. 
Marvin, C. F., evaporimeter, 150. 

vapor tension, 112. 
Mass Curves, precipitation, 236. 



Mass Curves — Continued — 

rainfall-runoff relations, 493. 

runoff, Ashtabula River, 526. 

storage calculations, 518. 
Matthews, E. R., changes in English 

coast, 347. 
McAlpine, W. J., flood wave, 563. 
Measurement, precipitation, 187. 

precipitation, literature, 198. 

evaporation, 150., 

streamflow, 479, 482. 

stream, difficulties, 482. 
Menominee River, duration curves, 
Merrimac River, flood wave, 563. 

rainfall-runoff relations, 498, 
503. 
Merrill, Wis., intense rainfall, 250. 
Meteorological laws, 10. 
Meyer, A. F., comparative stream- 
flow, 515. 

ground flow, 496. 

runoff computation, 513. 
Miami Conservancy District, exces- 
sive rainfall, 270. 

factor of safety, 594. 

major storms, time, area, and 
depth, 277. 

storm frequency studies, 275. 
Miami River, flood, 176, 489, 550, 557. 

flood frequency, 569. 

flood of 1913, 176. 

valley storage, 576. 
Milham. W. I., evaporation measure- 
ment, 150. 
Milwaukee, precipitation, 212. 

pumpage, 474. 
Minneapolis, artesian well, 363. 
Minnesota, drift sections. 380. 

glacial lakes, 378. 

Potsdam formation. 363. 
Mineral content, ground water, 411. 

disolved by water, 32, 353, 411. 
Mines, water in, 36. 
Mississippi River, delta, 348. 

floods. 550. 

floods, cause of, 551. 561. 

flood frequency, 570. 

flood height increase, 572. 

preglacial, 332, 375. 

Russell's formula, 509. 



Index. 



637 



Mississippi River — Continued — 

valley storage, 575. 

Devonian Period, 367. 

earthquake, 320. 

erosion of strata, 3G9. 
Mississippi Valley, geology, 360. 

Lower Magnesian Limestone, 
366. 

mineral water, 414. 
Missouri, drainage runoff, 585. 

Ozark uplift, 367. 
Moisture Atmospheric, altitude, 1 14. 

cloud, 125. 

distribution geographical, 121, 
152. 

distribution vertical, 119. 

humidity, 112. 

interchange between air and 
earth surface, 123. 

knowledge importance, 152. 

literature, 154. 

measurement, 150. 

source, 123, 163. 

temperature and humidity, 113. 

vapor tension, 112. 

weight per cubic foot, 112. 
Monterey, Mex., intense rainfall, 250. 
Monthly weather Review, 172, 194. 
Moore, W. L., precipitation, 161. 
Morgan, A. E., drainage district runoff, 
585. 

intense rainfall, study, 270. 
Mountain, effects, 164. 

see precipitation, altitude. 
Morains, glacial, 316, 377. 
Mt. Washington, rainfall, 287, 290, 
303. 

National Weather and Crop Bulletin, 

172. 
Natural laws, human agencies effect, 
12. 

limitations of, 2. 
Natural Sciences, progress in, 13. 
Navigation, 3. 

canals, 25. 

factors in investigation, 618. 

importance, 615. 

literature, 626. 

water supply for, 37, 477. 



New England, precipitation, 212. 

precipitation cycles, 215. 

rainfall and altitude, 287, 290. 
New Mexico, rainfall, 294. 
New Orleans, La., storm of 1915, 81. 
New York, Adirondack Region, 362. 

Silurian period, 367. 
Niagara Falls, erosion, 333. 

geology, 367. 

origin of, 329. 

recession, 330. 
Niagara Limestone, outcrop, 367, 3G9. 
Norway, rainfall, 285. 

Ocean, precipitation, effect, 166. 

source of atmospheric moisture.. 
164. 

Ocean currents, 31. 

cause, 89. 

effect on temperature, 89. 

literature, 109. 
Occurrence of water, 23. 
Ohio River, flood frequency, 569. 

Russell's formula, 509. 
Ohio Valley, Devonian period, 367. 

precipitation, cycles, 215. 
Oneota Limestone, 365. 
Ordovician period, 365. 
Orographic, precipitation, 161. 
Ozark uplift, 367. 

Pacific Coast, rainfall, 284, 286. 
Passaic River, flood, 6. 

Vermuele's formula, 510. 
Paris, Lieutenant, waves, 105. 
Pennsylvania, Carboniferous Period, 

368. 
Peshtigo River, comparative hydro- 
graphs, 537. 

physical conditions, 538. 
power plant, 474. 
rainfall, 538. 
Phenomena complex, 17. 
Physical conditions, 598. 
Physical variables, engineering, 478. 
Physiographical conditions, similiar 

ity, 13. 
Planetary circulation, see circulation 
atmospheric. 



638 



Ind 



ndex 



Pleistocene deposits, 386. 
Pollution, ground water, 415. 
Pondage, literature, 543. 
Popular River, Mont., minimum tem- 
perature, 82. 

Porosity, flow in soils, 420, 421. 

strata, 391. 
Porto Rico, precipitation, 176. 
Potsdam, outcrop extent, 365. 
sandstone, 362. 
water, mineral, 414. 
water supply, 365, 382. 
Precambrian Rock, 356. 
Precipitation, abundant, 156. 
amount evaporated, 164. 
amount necessary for runoff, 

497. 
artificial production, 185. 
atmospberic moisture, 152. 
average in .United States, 164. 
cause, 159, 165. 
caught by forest, 14V. 
classification, 160. 
consideration, practical, 156. 
convective, 159. 
cyclone effect, 62, 87. 
cyclonic, 161, 167, 176. 
data, 187, 243. 

accuracy, 190, 191. 

conclusions from. 159. 

high altitudes, 168. 

inadequate, 158, 159. 

sources. 172. 

study, 157. 

United States, 193. 

use, 157. 
deficient, 156. 
desert, 33. 
disposal of, 34, 164. 
distant from supply, 159. 
due to cyclonic wind, see preci- 
pitation, cyclonic, 
engineering, influences, 157. 
estimating quantity, 196. 
evaporation relations. 141. 
factors of intensity, 289. 
factors modifying, 165. 
forest, effect. 169. 
geographical distribution, 172. 



Precipitation — Continued — 

geographical variation, 33. 

hurricane, 175. 

interior lands, 164. 

intense, see rainfall, intense. 

island and coast, 164. 

isohyetals, 198. 

literature, 185. 

local similiarity, 158. 

measurement, 187. 

measurement literature, 198. 

mountain effect, 164, 166. 

occurrence, 172. 

oceans and lakes, effect, 166. 

orographic, 161, 447. 

probable future, 157. 

production, artificial, 185. 

records, dependability, 195. 

records, published, 193. 

records, see precipitation, data 

source, 159. 

source of surface waters, 33. 

streamflow, annual relation, 
496. 

streamflow, effect, 158. 

streamflow, factors, 441. 

streamflow literature, 470. 

streamflow relations, see rain- 
fall-runoff. 

thunder storms, 183. 

variation, 33. 

water supply, maximum, 466. 

water supply, minimum, 469. 

water supply, source, 156. 

water supply, variable, 468. 

wind effect, 84, 166. 

see also rainfall. 
Precipitation, altitude, Altapass. N. 
C, 302. 

altitude, effect, 167. 

altitude of maximum, 168. 

Applachians, 284. 

Arizona, 295, 307. 

Austria, 306. 

Catskills; 290. 

complications in relations, 290, 
292. 

data and records, 283. 

fallacy of general conclusions, 
307. 



Ind 



ex. 



639 



Precipitation, altitude — Continued — 

formulas for, 284. 

formulas for estimate, 307. 

French Alps, 306. 

Germany, 285. 

Himalayas, 285. 

importance of subject, 283. 

literature, 307. 

Los Angeles storm, 302. 

local relations, 285. 

Mt. Lowe, Cal., 303. 

New England, 287. 

Norway, 285. 

occurrence of greatest rainfall, 
284. 

Pacific Coast, U. S., 284, 286. 

rules for estimates, 304. 

Sierra Nevada, 284. 

single storm, 301. 

Southern California, 291. 

Utah, 298. 

Western Ghauts, India, 284. 
Precipitation annual, Arizona, table 
of average, 295. 

average U. S., 200. 

causes of variation, 202. 

change in, 208. 

cycles, 208, 212, 214. 

distribution in U. S., 201. 

extremes, 203. 

extreme variations, 215. 

factors, 202. 

future expectancy, 216. 

literature, 226. 

local variation, 203, 207. 

maximum periods, 212. 

mean, time to establish, 212. 

occurrence of greatest, 284. 

probabilities, 219. 

progressive means, 208. 

study detail, 212. 

variation, 202, 213. 

Wisconsin, 203. 
Precipitation, seasonal, analysis, 237. 

distribution in U. S., 228. 

irrigation, necessity for, 229. 

Madison, monthly, 233. 

mass diagrams, 236. 

seasonal divisions of year, 236. 

stream flow, effect, 240. 



Precipitation, seasonal — Continued — 

variation, 228. 

variation, cause, 232. 

variations, local, 232. 

water year, 240. 
Preglacial drainage, 373, 450. 
Preglacial lakes, 342. 
Prejudice, personal, 15. 
Pressure atmospheric, altitude, 54. 

cause, 51. 

circulation of atmosphere, 51, 
57. 

cold waves, 81. 

cyclone, 63. 

distribution, 51, 58. 

intensity, 53. 

movements of centers, 87. 

seiches, 99. 

storms, 66. 

temperatures, 116. 

tornado, 75. 

tracks of high, 81. 

variations, 51, 55. 
Probability, flood frequency, 570. 
Probabilities, law of, precipitation, 

219. 
Projects, control of water, 598. 

purpose, 597. 

utilization of water, 598. 
Protection, flood, see flood. 
Pseudo scientists, 17. 
Public, water supply, 37 ,473. 

Rafter, G. W., rainfall runoff, 498, 505. 

water year, 502. 
Railway, culvert capacity, 589. 

flood structures, 544. 
Rainfall, Ashtabula River, 528. 

basis of estimates, 13. 

coefficients, 225. 

distribution of, 18. 

effect on stream flow, 491. 

floo deflect, 566, 579. 

annual, Florida, 249. 

forests, 18. 

Madison, Wis., 9. 

annual, Ohio, 249. 

Peshtigo River, 538. 

pollution of, 32. 

purity, 32. 



640 



Ind 



ex- 



Rainfall — Continued — 

records, see precipitation. 

stations, 13. 

streamflow, 490. 

variations, 9. 

Wisconsin, 249. 

Wisconsin floods, 1911, 553. 

see precipitation. 
Rainfall intense, Altapass, X. C, 247, 
302. 

Alexandria, La., 279. 

area, 243, 277. 

Cambridge, O., 245. 

cyclonic, 250. 

data, application of, 271. 

depth limitations, 274. 

duration, 243. 

eastern U. S., 270. 

extreme conditions, 27S. 

factors of magnitude, 243. 

Florida, 249. 

formulas, 259, 262. 

frequency, 244, 249, 250, 253, 
255, 275, 279. 

geographical limitations, 272. 

Guinea, Va., 246. 

hurricane, 249. 

ignorance of frequency, 280. 

information limitations, 245. 

intensity, 243. 

large areas, 266. 

Lee Roy, N. Y., 245. 

literature, 280. 

local intensities, 250, 259. 

longer duration, 263. 

Los Angeles, Cal., 302. 

Madison, Wis., 253, 279. 

maximum intensity, 257. . 

maximum in Northern U. S., 
261. 

maximum in Wisconsin, 260. 

major storms, 277. 

Merrill, Wis., 250. 

Monterey, Mex., 250. 

occurrence, 244. 

probable frequency, 275. 

probability, 244. 

records, 243. 

recording maxmium intensity, 
266. 



Rainfall, intense — Continued 

seasonal limitations, 273. 

semi-arid regions, 250. 

source of information, 247. 

St. Paul, Minn., 251. 

study, importance, 243. 

study of Miami conservancy, 
270. 

table of in U. S., 247. 
Rainfall and Runoff, 18. 

annual relations, 496. 

annual variations, 503. 

Ashtabula River, 532. 

determining relations, 498. 

diagrams, 500. 

discordance, 508. 

empirical expressions, 502. 

literature, 543. 

percentage estimates, 502. 

periodic relations, 505. 

periodic variations, 503. 

seasonal variations, 503. 
Raingage, exposure, 189. 

description, 187. 

distribution in U. S., 245. 

non-recording, in use, 247. 

recording, in use, 248. 

uncertainty in intense rainfall, 
266. 
Kapids, origin, 327. 
Rating curve, 479. 
Reason, deductive, 15. 

inductive, 15. 

process of, 15. 
Reclamation Service, drainage, 622. 

irrigation projects, 606. 

Hondo, project, 8. 

Salt River, project, 607. 

use of water, 476. 
Records, rainfall, see precipitation. 
Regnault, vapor tension, 112. 
Relations, quantitative, 16. 

rainfall and runoff, 18. 
Reservoir, forest bed, 455. 
Retardation, flood waves, 494. 
Retention, constancy, 496. 

definition, 491. 

rainfall streamflow, 491. 

Vermuele's formula, 510. 



Ind 



ex. 



641 



Rhine River, flood frequency, 569. 
Rippl, storage calculations, 517. 
Rivers, base level, 381. 

constriction of channel, 41. 

discharge, see stream flow. 

disappearing, 399, 403. 

diversion by glaciers, 375, 380. 

flood plains of, 39. 

glacial diversion ,450. 

literature, 350. 

navigation, 617. 

obstructions in, 4G5. 

underflow, 407, 447, 450. 
River Warren, 379. 
Rock, absorption, 391. 

Algonkian, 356. 

Archean, 356. 

characteristics of strata, 369. 

disintegration, 310. 

envelopes of earth, 44. 

Laurentian, 358. 

modifications of strata, 369. 

Precambrian, 356. 

structure, 311. 
Rockford, 111., water supply, 602. 
Rock River, preglacial, 332. 
Rothamsted, England, soil evapora- 
tion, 141. 
Runoff, analysis, 514. 

city areas, 584. 

culvert design, 589. 

drainage districts, 585. 

estimating, 509. 

factors, 509. 

formulas, 509. 

formulas, city areas, 586. 

formula derivation, 591. 

ground water, 390. 

see stream flow 
Russell, J. S., flood wave, 563. 
Russell, Thomas, runoff formulas, 589. 
Sacramento River, floods, 557. 
Safety Factor, 478. 

flood flows, 580. 

engineering, 11. 

magnitude of, 593. 
Salt River project, 607. 
San Francisco Earthquake, 320. 
Sanitary water, 353. 
Saturation, depth, 393. 

Hydrology — 41 



Sault Ste. Marie Canal, 617. 
Science, Natural, progress in, 13. 

relations of hydrology, 1. 
Scientists, psuedo, 17. 
Schott, C. A., precipitation data, 193. 
Seas as reservoirs, 35. 
Seasonal divisions of year, 236. 
Sedimentary Rock, 354. 
Sediment suspended in Rivers, 324. 
Seepage, 31, 34, 447. 

ground water, 393, 395, 460. 

irrigated land, 465. 

streamflow factor, 448, 469. 

underground flow, 467. 

vegetation effect, 455. 
Seiches, cause, 99. 
Seine River, flood frequency, 569. 
Selection of water supply, 37. 
Settlement, effect of purity of water, 
33. 

hydrological influences, 3. 
Sewerage, factors in investigation. 
619. 

importance, 619. 

literature, 626. 

runoff, city areas, 584. 

flood provision, 593. 

improper, 9. 
Shoshone Dam, storage, 463. 
Sierra Nevada, rainfall, 284. 
Signal Service, 13. 

rainfall records, 194. 
Silurian Period, 367. 
Similiarity in hydrological condi- 
tions, 11. 
Simplicity of phenomena, 17. 
Sink, limestone, 371, 403. 
Slichter, C. S., ground water flow, 419, 

423. 
Slides, land, due to water, 36. 
Smith, G. E. P., rainfall and altitude, 

307. 
Smithsonian Institute, rainfall rec- 
ords, 193. 
Snow, evaporation, 135, 455. 
Snowfall, measurement, 193. 
Sources water supply, 602. 
Springs, artesian, 383. 

Barton, Austin, Tex., 401. 

cause, 399. 



642 



Ind 



ex 



Springs — Continued — 

hot, 411. 

intermittent, 403. 

Tuscumbia, Alabama, 403. 
Stevenson, Thomas, height of waves, 

104. 
Stewart, C. B., flood flows, 584. 

ground flow, 494. 
St. Anthonys Falls, origin, 330. 
Si. Paul, Minn., intense rainfall, 251. 

intense rainfall frequency, 255. 
St. Peter's Sandstone, 36 j. 

water supply, 382. 

outcrop of, 36G. 
Stoney River Dam, W. Va., 6. 
Storage, artificial, 461. 

calculations, 517. 

evaporation effect, 152. 

flood height effect, 5C5, 574. 

forest bed, 455. 

geology, effect, 352. 

Hill's method, 520. 

large, 517. 

limited, 522. 

literature, 543. 

moderate, 520. 

natural, 456. 

problems, 517. 

retention, 491. 

Rippl's method, 517. 

streamflow, effect of, 494. 

subsurface, 459. 

surface, 456. 

valley, 575. 

water power, 614. 

water supply, maximum, 467. 
Storms, tropical, frequency, 78. 

literature, 88. 

cyclonic, movement, 64. 

number annually, 73. 

translation of center, 64. 

thunder, see thunder storm. 

see winds. 
Strata, elevation of outcrops, 373. 

geological, 369. 
Stream control, 463. 

economics, 516. 

magnitude of works, 516. 
Stream, contamination of, 33. 

growth of, 325. 



Streams — Continued — 

literature, 350. 

origin of falls and rapids, 327 

profiles, 325. 

sediment in 324. 

transportation of detritus, 322 

work of, 325. 
Stream flow, analysis, 514. 

Ashtabula River, 425, 534. 

average annual, 484. 

comparative, 484, 535. 

contiguous streams, 486. 

control, 463. 

cultivation, 454. 

data, accuracy, 483. 

data, use, 483. 

drainage, 453. 

drainage area, 443. 

equalized, 466. 

estimating, see runoff. 

evaporation ,152, 448, 453. 

extremes, 434, 470, 484. 

factors, 441. 

flood, 266. 

flood wave retardation, 494. 

forest, 470. 

forest, literature, 471. 

geographical conditions, 443. 

geology, 309, 446. 

ground water, 460. 

hydraulics, 480. 

lag in, 491, 505. 

lakes and swamps, 457. 

large storage, 517. 

limited storage, 522. 

variations, literature, 508. 

literature, estimating, 543. 

maximum, 243. 

measurement, 479. 

measurement, difficulties, 482. 

measuremen terrors, 482. 

meteorological conditions, 450. 

moderate storage, 520. 

natural storage 456. 

occurrence, 433. 

percolation, 448. 

precipitation, 34, 441. 

precipitation, effects, 157. 

precipitation, extremes, 489. 

precipitation intensity, 241. 



Index. 



643 



Stream flow — Continued — 

precipitation literature, 471. 

precipitation, quantity, 241. 

problems of, 435, 473, 51G. 

rainfall, 18, 490. 

rainfall, annual relations, 4%. 

rainfall, intense, effect, 243. 

rainfall, minimum for, 497. 

rainfall relations, 164, 490. 

records, 14. 

rainfall relations, see rainfall 
runoff. 

rule for runoff, 500. 

seasonal rainfall, effect, 240. 

seasonal variation, 489. 
Stream flow, source, 432. 

storage artificial, 463. 

storage effect, 494. 

storage, natural, 456. 

study, 432. 

topography, 446. 

under flow, 407, 447, 450. 

unit basis, 4S4. 

use, 463. 

variations, 9, 434, 468, 473. 

variations, different streams, 
485. 

variations, same stream, 486. 

value of knowledge, 484. 

value of studies, 515. 

vegetation, 454. 

water supply, 433, 456. 

water supply, minimum, 469. 

water supply, variations, 467. 

see floods. 

see runoff. 
Stream Gaging, 479. 

literature, 508. 
Study Hydrology, necessity for, 41. 
Sudbury River, Vermuele's formula, 

510. 
Surface, evaporation factor, 126. 

streamflow factor, 453. 

water, 29. 

water, disposal of, 34. 

water, evaporation of, 35, see 
also Evaporation. 

water, importance of, 34. 

water, movements of, 34. 



Surface — Continued — 

water, surface and subsurface, 
34. 
Suspension, water vapor, 125. 
Swamp, drainage of, 36. 

drainage runoff, 585. 

streamflow factor, 457. 

lands in United States, 621. 

Talbot, A. N., intensity of rainfall, 

259. 
Tate, Thomas, evaporation factors, 

148. 
Tax, procuring funds, 597. 
Temperature, boiling, 133. 

factor in evaporation, 126. 

flow of ground water, 422. 

ground water, 409. 

latitude effects, 49. 

minimum, 81. 

streamflow factor, 450. 

under various conditions, 130. 
Temperature atmospheric, 40. 

altitude effect, 47, 114. 

altitude gradients, 115. 

cause of, 47. 

cold waves, 81. 

distribution over earth, 51. 

diurnal effect, 47, 48. 

effect of ocean currents, 89. 

effect of sea, 49. 

hot waves, 84. 

latitude effect, 47. 

ranges, 46. 

region of constant, 45. 

seasonal effect, 47. 

seasonal range, 49. 

vapor tension effect, 130. 

variation, 48. 

wind effect, 47. 
Temperature, lake, effect on currents, 

90. 
Temperature, soil, changes, 48. 
Temperature, water, ocean surface, 
49. 

sea, 49. 

underground, 409. 

wells, 409. 
Testing wells, 424. 



644 



Ind 



ex- 



Texas, artesian section, 405. 

Barton Spring, 401. 

hurricanes, 79. 
Thunder Storm, distribution, 183. 

expectancy, 183. 

occurrence, 179. 
Theories .fundamental, 43. 
Tides, 31. 

Bay of Fundy, 93. 

cause, 92. 

complicated, 96. 

cotidal lines, 96. 

height of, 93. 

literature, 109. 

predictions, 96. 

progress, 92. 

protection against, 41. 

tide table, 97. 

wind tides, 98. 
Time, geological, 355. 
Topography, causes of changes, 310. 

glacial, 331, 375, 381. 

hydrological influence, 309. 

influence of water, 23. 

conditions, local influences. IS. 

precipitation, 447. 

preglacial, 373. 

rainfall effect, see precipita 
tion, altitude. 

stream flow factor, 446. 
Tornadoes, see wind. 
Trade winds, moisture, 121. 
Transpiration, 31. 

estimates for, 147. 
Transportation, factors of, 310. 

ice 323. 

stream, 314, 322. 

stream, literature, 350. 

wind, 323. 
Trenton Limestone, 365, 366. 
Turneaure. F. E., intense rainfall, 
263. 

well hydraulics, 425. 
Tweedale, W., water consumption by 
vegetation, 144. 

Underground drainage, 371. 
United States, 

Census, irrigation statistics, 
605. 



United States — Continued — 

Dept. Agriculture, drainage 

investigations, 585. 
Geol. Survey, data by, 484. 

stream gagings, 483. 

warning by, 485. 

work of, 14. 
navigable waters, 617. 
precipitation, annual, 200. 
Reclamation Service projects, 

606. 
see Reclamation Service, 
swamp lands, 621. 
water power developments in, 

614. 
Weather Bureau, data by, 484. 
see Weather Bureau. 
Utah, 

evaporation, 137. 
Experiment Station, 
precipiattion, 168. 
rainfall, 298. 
Utilitarian, precipitation analyses, 

237. 
Utilization of water, 598. 

Vapor Tension, evaporation, effect, 
126, 127. 

temperature effect, 130. 

see moisture, atmospheric. 
Valley storage, 574. 
Variations, conditions, 13. 

hydrological phenomena, 9. 

precipitation, 9, 33. 

stream flow, 9. 
Vegetation, erosion, 456. 

soil evaporation, effect, 144. 

soil protection, 456. 

streamflow factor, 454. 

water consumption, 34, 144. 
Vermuele, C. C, ground flow, 496. 

runoff formulas, 510. 
Volcanic Rock, 354. 
Vulcanism, 318, 321. 

Warping, earths crust, 358, 371. 
Waste disposal, 38. 
Water, activity of, 23. 

agriculture requirements, 25. 



Ind 



ex. 



645 



Water — Continued — 

area of surface of earth, 28. 
circulation of, 30. 
circulation causes, 31. 
cleanser, 32. 
commerce, 25. 
control of, 38. 
cleansing, 38. 
disposal of wastes, 38. 
erosion of soil, 38. 
land reclamation. 39. 
density, 90. 
destruction by, 28. 
envelope of earth, 44. 
essential to life, 23. 
existence above sea level, 35. 
existence below sea level, 35. 
geological change, 23. 
ground, see ground water, 
hard, 32. 
health effect, 23. 
mineralization, 32, 353. 
occurrence, 28, 33. 
occurrence, control and utiliza- 
tion, 23. 
organic impurities, 33. 
potable, 32. 

power and industry, 27. 
power source, 26, see also Wa- 
ter Power, 
projects for use and control, 

598. 
sanitary character, 353. 
settlement effect, 33. 
soft, 32. 
solution by, 32. 
source of, 30. 
spout, see wind, 
streams, 35. 

surface, see surface water, 
temperatures, ground, 409. 
temperatures, sea, 49. 
topographical change, 23. 
use of, 25. 
work of, 32. 
Water year, definition, 502. 

division, 240. 
Water Power, electrical transmission, 
28. 

failures, 613. 



Water Power — Continued — 
importance of, G12. 

investigations, G14. 
literature, 626. 
United States, 614. 
Water Supply, 474. 

adequacy of, 37. 
commercial uses, 37. 
considerations of, 599. 
demand variations, 474. 
equipment, 602. 
factors of, 603. 
failures, 8. 

first consideration, 37. 
forest reservoir, 455. 
geological formations, 355. 
geology, effect, 352. 
glacial drift, 382. 
ground water, 390. 
investigation, 603. 
irrigation, 476. 
literature, 625. 
maximum, 466. 
navigation, 477. 
necessity for, 36. 
Potsdam formation, 365, 382. 
power, 474. 

public, consideration of, 473. 
quality, 602. 
requirements in, 36. 
selection of, 37. 
sources, 602. 
St. Peter sandstone, 382. 
stream flow, 433. 
ultimate source, 150. 
underflow, 450. 
Water Table, above ground, 398. 
defined, 393. 
variation. 397. 
Waves, 31. 

classification, 102. 
depth, 108. 
effects, 10S. 
energy, 107, 109. 
erosion by, 314. 
flood, advance, 563. 
height of, 104. 
length of, 105. 
literature, 110. 
motion of, 103. 



646 



ind 



ex- 



Waves — Continued — 
tide, 92. 
velocity, 105. 
wind effect, 84. 
Weather Bureau, 194. 

districts of cyclone origin, 05. 
rainfall stations, 13. 
rain gage location, 190. 
stations in U. S., 245. 
weather map, 169. 
work of, gage heights, 14. 
Weathering, rock, 312. 
Weather forecasting, 86. 
Weather Map, 87, 109. 
Weather predictions, long range, IS. 
Wells, cone of depression, 425. 
defined, 423. 
flowing, 383. 
hydraulics, 425. 
interference, 426. 
literature, 430. 
permanency, 429. 
test of, 424. 

variation in water level, 42G. 
water of, 36. 
yield, 423, 424. 
Western Ghauts, India, rainfall, 284. 
West Indian Hurricane, 78. 

see wind. 
West Virginia, temperature of wells, 

409. 
Winchell, Prof. W. H., Potsdam for- 
mation, 363. 
Wind, anticyclone, circulation, 64. 
anti trade, 59. 
atmospheric moisture, 123. 
belt of calms, 59. 
Chinook, 62. 
cyclonic, 62. 
circulation, 63. 
cold waves, 81. 
districts of Weather Bureau, 

65. 
hot waves, 84. 
movements, 65. 
origin, 63. 
precipitation, 87. 
tracks, 65. 
dry, cause of, 284. 
evaporation, 84, 132. 



Wind — Continued — 

factor in evaporation, 126. 
Foehn, 62. 
hurricane, 62. 

Galveston, Tex., 79. 

movements, 78. 

New Orleans, 81. 

origin, 77. 

wind tides, 99. 
hydrological effects, 84. 
irregular, 62. 
land and sea, 62. 
literature, 88. 
local altitude effects, 71. 

diurnal, 71. 

influences, 66. 

movement, 66. 

prevailing direction, 73. 
Mistral, 62. 
Monsoon, 62. 
mountain and valley, 62. 
periodic, 59. 
permanent, 59. 

precipitation, 84, 166, 168, 284. 
precipitation measurement, 189, 

191. 
prevailing in U. S., 66. 
Prevailing Westerlies, 59. 
rainfall effect, 284. 
seasonal changes, 62. 
Sirocco, 62. 

storm center translation, 64. 
storm, circulation, 64. 
streamflow factor, 451. 
variation with altitude, 133. 
velocity in U. S., 71. 
thunder storm, 62. 
tides due to, 98. 
topographical effects, 62. 
tornado, 62. 

appearance, 75. 

cause, 75. 

dimensions, 73. 

fore casting, 76. 

occurrence, 73. 
trade, 59. 

transportation of detritus, 323. 
tropical hurricanes, 76. 
tropical storm frequency, 78. 
typhoon, 62, 76. 



Ind 



ex. 



647 



Wind — Continued — 

waterspout, 76. 

waves, 84. 

weather forecasting, 86. 
Wisconsin, 

artesian area, 405. 

erosion in, 369. 

floods, 553, 584. 

glacial lakes, 378. 

ground water quality, 412. 

Hudson River shale, 369. 

Lower Magnesian Limestone, 
365. 

Potsdam formation, 362. 

precipitation, 203, 211. 



Wisconsin Continued — 

precipitation cycles, 215. 

Wisconsin River, duration curves, 
540. 

flood wave, 494. 

gage heights, 489. 

rainfall runoff relations, 491, 
505. 

runoff, 448. 

storage effects, 461, 494. 
Wisconsin, Silurian period, 367. 
Woolny, transpiration, 147. 

Zon, transpiration, 147. 




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